# ABINIT, PAW input variables:

## List and description.

This document lists and provides the description of the name (keywords) of the input variables for runs based on the Projector Augmented Waves methodology, to be used in the main input file of the abinis code.

The new user is advised to read first the new user's guide, before reading the present file. It will be easier to discover the present file with the help of the tutorial.

When the user is sufficiently familiarized with ABINIT, the reading of the ~abinit/doc/users/tuning file might be useful. For response-function calculations using abinis, please read the response function help file

##### Copyright (C) 1998-2009 ABINIT group (DCA, XG, RC)
This file is distributed under the terms of the GNU General Public License, see ~abinit/COPYING or http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

Goto : ABINIT home Page | Suggested acknowledgments | List of input variables | Tutorial home page | Bibliography

Help files : New user's guide | Abinis (main) | Abinis (respfn) | Mrgddb | Anaddb | AIM (Bader) | Cut3D | Optic | Mrgscr

Files that describe other input variables:

- Basic variables, VARBAS
- Developper variables, VARDEV
- File handling variables, VARFIL
- Geometry builder + symmetry related variables, VARGEO
- Ground-state calculation variables, VARGS
- GW variables, VARGW
- Internal variables, VARINT
- Parallelisation variables, VARPAR
- Response Function variables, VARRF
- Structure optimization variables, VARRLX
- Wannier90 interface variables, VARW90

### Content of the file : alphabetical list of PAW input variables.

A.
B. bxctmindg
C.
D. dmatpawu dmatpuopt dmatudiag
E.
F.
G.
H.
I. iboxcut
J. jpawu
K.
L. lpawu lexexch
M. mqgriddg
N. ngfftdg
O.
P. pawcpxocc pawecutdg pawlcutd pawlmix pawmixdg pawnhatxc pawnphi pawntheta pawnzlm pawoptmix pawovlp pawprtden pawprtdos pawprtvol pawspnorb pawstgylm pawusecp pawxcdev prtfc prtefg prtnabla ptcharge
Q. quadmom
R.
S. spnorbscl
T.
U. usedmatpu upawu useexexch usepawu
V.
W.
X.
Y.
Z.

bxctmindg
Mnemonics: BoX CuT-off MINimum for the Double Grid (PAW)
Characteristic:
Variable type: real parameter
Default is 2.0
Relevant only when usepaw=1.
The box cut-off ratio is the ratio between the wavefunction plane wave sphere radius, and the radius of the sphere that can be inserted in the FFT box, in reciprocal space.
If the density was generated only from wavefunctions, this ratio should at least two in order for the density to be exact. If one uses a smaller ratio, one will gain speed, at the expense of accuracy. In case of pure ground state calculation (e.g. for the determination of geometries), this is sensible. However, the wavefunctions that are obtained CANNOT be used for starting response function calculation.
However, some augmentation charge is always added in PAW, and even with the box cut-off ratio larger than two, the density is never exact. Sometimes, this ratio must be much larger than two for the computation to be converged at the required level of accuracy.
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dmatpawu
Mnemonics: initial Density MATrix for PAW+U
Characteristic:
Variable type: real array dmatpawu(2*max(lpawu)+1, 2*max(lpawu)+1, max(nsppol,nspinor), %natpawu)
where %natpawu is the number of atoms on which LDA/GGA+U is applied.
default is -10. (not defined)
Relevant only when usepaw=1, usepawu=1, usedmatpu/=0 for Ground-State calculations.
Gives the value of an initial density matrix used in LDA+U and kept fixed during the first abs(usedmatpu) SCF iterations.
Only components corresponding to lpawu angular momentum are requested.
Restriction: In order to use dmatpawu, lpawu must be identical for all atom types (or -1).
The occupation matrix is in the basis of real spherical harmonics Slm. Their are ordered by increasing m, and are defined e.g. in this paper. For the case l=2 (d states), the five columns corresponds respectively to (the normalisation factor has been dropped)

- m=-2, xy
- m=-1, yz
- m=0, 3z^2-r^2
- m=1, xz
- m=2, x^2-y^2

dmatpawu must always be given as a "spin-up" occupation matrix (and eventually a "spin-down" matrix). Be aware that its physical meaning depends on the magnetic properties imposed to the system (with nsppol, nspinor, nspden):

- Non-magnetic system (nsppol=1, nspinor=1, nspden=1):
  One (2lpawu+1)x(2lpawu+1) dmatpawu matrix is given for each atom on which +U is applied.
  It contains the "spin-up" occupations.
- Ferromagnetic spin-polarized (collinear) system (nsppol=2, nspinor=1, nspden=2):
  Two (2lpawu+1)x(2lpawu+1) dmatpawu matrixes are given for each atom on which +U is applied.
  They contain the "spin-up" and "spin-down" occupations.
- Anti-ferromagnetic spin-polarized (collinear) system (nsppol=1, nspinor=1, nspden=2):
  One (2lpawu+1)x(2lpawu+1) dmatpawu matrix is given for each atom on which +U is applied.
  It contains the "spin-up" occupations.
- Non-collinear magnetic system (nsppol=1, nspinor=2, nspden=4):
  Two (2lpawu+1)x(2lpawu+1) dmatpawu matrixes are given for each atom on which +U is applied.
  They contains the "spin-up" and "spin-down" occupations (defined as n_up=(n+|m|)/2 and n_dn=(n-|m|)/2), where m is the integrated magnetization vector).
  The direction of the magnetization (which is also the direction of n_up and n_dn) is given by spinat.
  Warning: unlike collinear case, atoms having the same magnetization magnitude with different directions must be given the same occupation matrix;
  the magnetization will be oriented by the value of spinat (this is the case for antiferro-magnetism).
- Non-collinear magnetic system with zero magnetization (nsppol=1, nspinor=2, nspden=1):
  Two (2lpawu+1)x(2lpawu+1) dmatpawu matrixes are given for each atom on which +U is applied.
  They contain the "spin-up" and "spin-down" occupations;
  But, as "spin-up" and "spin-down" are constrained identical, the "spin-down" one is ignored by the code.

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dmatpuopt
Mnemonics: Density MATrix for PAW+U OPTion
Characteristic:
Variable type: integer parameter
default is 2
Relevant only when usepaw=1 and usepawu=1
This option governs the way occupations of localized atomic levels are computed:

- dmatpuopt=1: atomic occupations are projections on atomic orbitals (Eq. (6) of PRB 77, 155104 (2008)).
- dmatpuopt=2: atomic occupations are integrated values in PAW spheres of angular-momentum-decomposed charge densities (Eq. (7) of PRB 77, 155104 (2008)).
- dmatpuopt=3: only for tests

In the general case dmatpuopt=2 is suitable. The use of dmatpuopt=1 is restricted to PAW datasets in which the first atomic wavefunction of the correlated subspace is a normalized atomic eigenfunction.
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dmatudiag
Mnemonics: Density MATrix for paw+U, DIAGonalization
Characteristic:
Variable type: integer parameter
default is 0
Relevant only when usepaw=1 and usepawu=1 and for Ground-State calculations.
This option can be used to diagonalize the occupation matrix Nocc_{m,m'}.
Relevant values are:

- 0: desactivated.
- 1: occupation matrix is diagonalized and printed in log file at each SCF cycle (eigenvectors are also given in the log file).
- 2: for testing purpose.

Not yet available for nspden=4.
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iboxcut
Mnemonics:
Characteristic:
Variable type: integer parameter
Default is 0
Concern all summations in the reciprocal space and is allowed in PAW and norm-conserving.

- if set to 0 all reciprocal space summations are done in a sphere contained in the FFT box.
- if set to 1 all reciprocal space summations are done in the whole FFT box (useful for tests).

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jpawu
Mnemonics: value of J for PAW+U
Characteristic: ENERGY
Variable type: real array jpawu(ntypat)
default is 0
Relevant only when usepaw=1, and usepawu=1.
Gives the value of the screened exchange interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.
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lexexch
Mnemonics: value of angular momentum L for EXact EXCHange
Characteristic:
Variable type: integer array lexexch(ntypat)
default is -1
Activated if useexexch is equal to 1.
Give for each species the value of the angular momentum (only values 2 or 3 are allowed) on which to apply the exact exchange correction.
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lpawu
Mnemonics: value of angular momentum L for PAW+U
Characteristic:
Variable type: integer array lpawu(ntypat)
Default is -1
Activated if usepawu is equal to 1 or 2.
Give for each species the value of the angular momentum (only values 2 or 3 are allowed) on which to apply the LDA+U correction.

- If equal to 2 (d-orbitals) or 3 (f-orbitals), values of upawu and jpawu are used in the calculation.
- If equal to -1: do not apply LDA+U correction on the species.

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mqgriddg
Mnemonics:
Characteristic: DEVELOP
Variable type: integer parameter
Default is 3001
Maximum number of wavevectors used to sample the local part of the potential, in PAW. Actually referred to as mqgrid_vl internally. Should change name to the latter ... See also mqgrid
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ngfftdg
Mnemonics: Number of Grid points for Fast Fourier Transform : Double Grid
Characteristic:
Variable type: integer array ngfftdg(3)
Default is 0 0 0 (so, automatic selection of optimal values)
Relevant only when usepaw=1.
This variable has the same meaning as ngfft (gives the size of fast Fourier transform (fft) grid in three dimensions) but concerns the "double grid" only used for PAW calculations.
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pawcpxocc
Mnemonics: PAW - use ComPleX rhoij OCCupancies
Characteristic:
Variable type: integer parameter
Default is 1, except for Ground-state static calculations (optdriver=0, ionmov<6) with spin-orbit coupling (pawspnorb=1), density mixing (iscf>=10) and time-reversal symmetry desactivated for k-points (kptopt/=1 or 2)
Relevant only when usepaw=1.
When pawcpxocc=2, PAW augmentation occupancies are treated as COMPLEX; else they are considered are REAL.
This is needed when time-reversal symmetry is broken (typically when spin-orbit coupling is activated).
Note for ground-state calculations (optdriver=0):
The imaginary part of PAW augmentation occupancies is only used for the computation of the total energy by "direct scheme"; this only necessary when SCF mixing on potential is chosen (iscf<10).
When SCF mixing on density is chosen (iscf>=10), the "direct" decomposition of energy is only printed out without being used. It is thus possible to use pawcpxocc=1 is the latter case.
In order to save CPU time, when molecular dynamics is selected (ionmov>=6) and SCF mixing done on density (iscf>=10), pawcpxocc=2 is (by default) set to 1.
When pawcpxocc=1, "direct" decomposition of total energy cannot be printed out.
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pawecutdg
Mnemonics: PAW - Energy CUToff for the Double Grid
Characteristic: ENERGY
Variable type: real parameter
Default is -1, so pawecutdg MUST be specified for PAW calculations.
Needed only when usepaw=1.
Define the energy cut-off for the fine FFT grid (the "double grid", that allows to transfer data from the normal, coarse, FFT grid to the spherical grid around each atom).
pawecutdg must be larger or equal to ecut. If it is equal to it, then no fine grid is used. The results are not very accurate, but the computations proceed quite fast.
For typical PAW computations, where ecut is on the order of 15 Ha, pawecutdg should be on the order of 40 Ha. Choosing a larger value should not increase the accuracy, but does not slow down the computation either, only the memory. The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.
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pawlcutd
Mnemonics: PAW - L angular momentum used to CUT the development in moments of the Densitites
Characteristic:
Variable type: integer parameter
Default is 10
Relevant only when usepaw=1.
The expansion of the densities in angular momenta is performed up to l=pawlcutd.
Note that, for a given system, the maximum value of pawlcutd is 2*l_max, where l_max is the maximum l of the PAW partial waves basis.
The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.
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pawlmix
Mnemonics: PAW - maximum L used in the spherical part MIXing
Characteristic:
Variable type: integer parameter
Default is 10
Relevant only when usepaw=1.
The choice made for this variable determine how the spherical part of the density is mixed during electronic iterations.
Only parts of (rhoij quantities) associated with l angular momenta up to l=pawlmix are mixed. Other parts of augmentation occupancies are not included in the mixing process.
This option is useful to save CPU time but DOES have a bearing on the numerical accuracy of the results.
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pawmixdg
Mnemonics: PAW - MIXing is done (or not) on the (fine) Double Grid
Characteristic:
Variable type: integer parameter
Default is 0 if npfft=1 (else 1)
Relevant only when usepaw=1.
The choice made for this variable determines the grid on which the density (or potential) is mixed during the SCF cycle.
- If pawmixdg=1 the density/potential is mixed in REAL space using the fine FFT grid (defined by pawecutdg or ngfftdg).
- If pawmixdg=0 the density/potential is mixed in RECIPROCAL space using the coarse FFT grid (defined by ecut or ngfft). Only components of the coarse grid are mixed using the scheme defined by iscf; other components are only precondionned by diemix and simply mixed.
This option is useful to save memory and does not affect numerical accuracy of converged results. If pawmixdg=1, density and corresponding residual are stored for previous iterations and are REAL arrays of size nfftdg. If pawmixdg=0, density and corresponding residual are stored for previous iterations and are COMPLEX arrays of size nfft. The memory saving is particulary efficient when using the Pulay mixing (iscf=7 or 17).
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pawnhatxc
Mnemonics: PAW - Flag for exact computation of gradients of NHAT density in eXchange-Correlation.
Characteristic:
Variable type: integer parameter
Default is 1
Needed only when usepaw=1.
Relevant only when a GGA exchange-correlation functional is used.
When this flag is activated, the gradients of compensation charge density (n_hat) are exactly computed (i.e. analytically); when it is desactivated, they are computed with a numerical scheme in reciprocal space (which can produce inaccurate results if the compensation charge density is highly localized).
As analytical treatment of compensation charge density gradients is CPU time demanding, it is possible to bypass it with pawnhatxc=0; but the numerical accuracy can be affected by this choice. It is recommended to test the validity of this approximation before use.
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pawnphi
Mnemonics: PAW - Number of PHI angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer parameter
Default is 13
Needed only when usepaw=1.
Number of phi angles (longitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawnphi and pawntheta.
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pawntheta
Mnemonics: PAW - Number of THETA angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer parameter
Default is 12
Relevant only when usepaw=1.
Number of theta angles (latitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawntheta and pawnphi.
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pawnzlm
Mnemonics: PAW - only compute Non-Zero LM-moments of the contributions to the density from the spheres
Characteristic:
Variable type: integer parameter
Default is 1
Relevant only when usepaw=1.
Concerns the computation of the contributions to the density from the spheres (named rho_1 - rho_tild_1).
If set to 0, all lm-moments of the sphere contributions to the density are computed at each electronic iteration.
If set to 1, only non-zero lm-moments of the sphere contributions to the density are computed at each electronic iteration (they are all computed at the first iteration then only those found to be non-zero will be computed ; thus the first iteration is more cpu intensive)
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pawoptmix
Mnemonics: PAW - OPTion for the MIXing of the spherical part
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.
When PAW is activated, the self-consistent requires the mixing of both the total potential (or density) and the "spherical part" (in fact the augmentation occupancies rho_ij).
The same mixing scheme is applied to the potential (density) and the spherical part. It is optimized in order to minimize a residual.
If pawoptmix=0 the residual is the potential (or density) residual.
If pawoptmix=1 the residual is a sum of the potential (or density) residual and the "spherical part" residual.
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pawovlp
Mnemonics: PAW - spheres OVerLap allowed (in percentage)
Characteristic:
Variable type: real parameter
Default is 5.0
Relevant only when usepaw=1.
When PAW is activated, a localized atomic basis is added to describe wave functions. Spheres around atoms are defined and they are IN PRINCIPLE not allowed to overlap. However, a small overlap can be allowed without compromising the accurary of results. Be aware that too high overlaps can lead to unphysical results.
With the pawovlp variable, the user can control the (voluminal) overlap percentage allowed without stopping the execution.
pawovlp is the value (in percentage: 0...100%) obtained by dividing the volume of the overlap of two spheres by the volume of the smallest sphere.
The following values are permitted for pawovlp:
- pawovlp<0. : overlap is always allowed
- pawovlp=0. : no overlap is allowed
- pawovlp>0. and <100. : overlap is allowed only if it is less than pawovlp %
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pawprtden
Mnemonics: PAW: PRinT total physical electron DENsity
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.
This input variable controls output of the full electron density in the PAW case. It is usesul when the user wants to post-process the electron density, say with AIM, or wants to visualize it. pawprtden=1 causes generation of a file _PAWDEN that contains the full valence charge density together with the PAW on-site contributions, and has the same format as the other density files. DO NOT use this variable to chain the density output from one calculation as the input to another, use prtden (see its description) for that.
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pawprtdos
Mnemonics: PAW: PRinT partial DOS contributions
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1 and prtdos=3.
This input variable controls the computation and/or printing of contributions to the PAW partial DOS in _DOS file(s):
+ Plane-waves contribution
+ "on-site" all-electron contribution (phi)
- "on-site" pseudo contribution (phi_tild).
If pawprtdos=0:
- The 3 contributions are computed; only the total partial DOS is output in _DOS file.
If pawprtdos=1:
- The 3 contributions are computed and output in _DOS file.
- In that case, integrated DOS is not output.
If pawprtdos=2:
- Only "on-site" all-electron contribution is computed and output in _DOS file.
- This a (very) good approximation of total DOS, provided that (1) the PAW local basis is complete, (2) the electronic charge is mostly contained in PAW spheres.
- In that case, the ratsph variable is automatically set to the PAW radius.
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pawprtvol
Mnemonics: PAW: PRinT VOLume
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.
Control print volume and debugging output for PAW in log file or standard output. If set to 0, the print volume is at its minimum.
pawprtvol can have values from -3 to 3:
- pawprtvol=-1 or 1: matrices rho_ij (atomic occupancies) and D_ij (psp strength) are printed at each SCF cycle with details about their contributions.
- pawprtvol=-2 or 2: like -1 or 1 plus additional printing: moments of "on-site" densities, details about local exact exchange.
- pawprtvol=-3 or 3: like -2 or 2 plus additional printing: details about PAW+U, rotation matrices of sphercal harmonics.
When pawprtvol>=0, up to 12 components of rho_ij and D_ij matrices for the 1st and last atom are printed.
When pawprtvol<0, all components of rho_ij and D_ij matrices for all atoms are printed.
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pawspnorb
Mnemonics: PAW - option for SPiN-ORBit coupling
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.
When PAW is activated, the spin-orbit coupling can be added without the use of specific PAW datasets (pseudopotentials).
If pawspnorb=1, spin-orbit will be added.
Note that only the all-electron "on-site" contribution to the Hamiltonian is taken into account; this a very good approximation but requires the following conditions to be fullfilled:
1- the~φi basis is complete enough
2- the electronic density is mainly contained in the PAW sphere
Also note that, when spin-orbit coupling is activated, the time-reversal symmetry might be broken.
The use of kptopt=1 or kptopt=2 is thus forbidden. It is adviced to use kptopt=3 (no symmetry used to generate k-points) or kptopt=4 (only spatial symmetries used to generate k-points).
Be careful if you choose to use kptopt=0 (k-points given by hand); Time-reversal symmetry has to be avoided.
An artificial scaling of the spin-orbit can be introduced thanks to the spnorbscl input variable.
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pawstgylm
Mnemonics: PAW - option for the STorage of G_l(r).YLM(r)
Characteristic:
Variable type: integer parameter
Default is 1
Relevant only when usepaw=1.
When PAW is activated, the computation of compensation charge density (so called "hat" density) requires the computation of g_l(r).Y_lm(r) factors (and cartesian derivatives) at each point of real space contained in PAW spheres. The number of atoms, of (l,m) quantum numbers and the sharpness of the real FFT grid can lead to a very big {g_l.Y_lm} datastructure. One can save memory by putting pawstgylm=0; but, in that case, g_l(r).Y_lm(r) factors a re-computed each time they are needed and CPU time increases.
Possible choices:
- pawstgylm=0 : g_l(r).Y_lm(r) are not stored in memory and recomputed.
- pawstgylm=1 : g_l(r).Y_lm(r) are stored in memory.
Note:
g_l(r) are shape functions (analytically known)
Y_lm(r) are real spherical harmonics
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pawusecp
Mnemonics: PAW - option for the USE of CPrj in memory (cprj=WF projected with NL projector)
Characteristic:
Variable type: integer parameter
Default is 1
Relevant only when usepaw=1.
When PAW is activated, the computation of cprj arrays is memory and time consuming.
When pawusecp=0, then the cprj are never kept in memory, they are recomputed when needed (this is CPU-time consuming). When pawusecp=1, then the cprj are computed once and then kept in memory.
Change the value of the keyword only if you are an experienced user (developper).
Remember: cprj = (WF_n .dot. p_i) (WF_n=wave function, p_i=non-local projector).
For the time being, only activated for RF calculations.
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pawxcdev
Mnemonics: PAW - choice for eXchange-Correlation DEVelopment (spherical part)
Characteristic:
Variable type: integer parameter
Default is 1
Relevant only when usepaw=1.

- If set to 0, the exchange-correlation term in the spherical part of energy is totally computed on the angular mesh
- If set to 1, the exchange-correlation term in the spherical part of energy is developed onto lm-moments at order 1
- If set to 2, the exchange-correlation term in the spherical part of energy is developed onto lm-moments at order 2 (can be memory/CPU consuming)

Be careful: GGA requires pawxcdev > 0
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prtfc
Mnemonics: PRinT Fermi Contact term
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.

- If set to 1, print the Fermi contact interaction at each nuclear site, that is, the electron density at each site. The result appears in the main output file (search for FC). Note that this calculation is different than what is done by cut3d, because it also computes the PAW on-site corrections in addition to the contribution from the valence pseudo-wavefunctions.

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prtefg
Mnemonics: PRint Electric Field Gradient
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.

- If set to 1, calculate the electric field gradient at each atomic site in the unit cell. Using this option requires quadmom to be set as well. Values written to main output file (search for Electric Field Gradient). If prtefg=1, only the quadrupole coupling in MHz and asymmetry are reported. If prtefg=2, the full electric field gradient tensors in atomic units are also given, showing separate contributions from the valence electrons, the ion cores, and the PAW reconstruction. If prtefg=3, then in addition to the prtefg=2 output, the EFG's are computed using an ionic point charge model. This is useful for comparing the accurate PAW-based results to those of simple ion-only models. Use of prtefg=3 requires that the variable ptcharge be set as well.
  The option prtefg is compatible with spin polarized calculations (see nspden) and also LDA+U (see usepawu).

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prtnabla
Mnemonics: PRint NABLA
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.

- If set to 1, calculate the matrix elements <Psi_n|-inabla|Psi_m> and write it in file _OPT to be read by the code conducti.

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ptcharge
Mnemonics: PoinT CHARGEs
Characteristic:
Variable type: real array ptcharge(ntypat)
default is 0
Relevant only when usepaw=1, and prtefg = 3 or greater.

- Array of point charges, in atomic units, of the nuclei. In the normal computation of electric field gradients (see prtefg) the ionic contribution is calculated from the core charges of the atomic sites. Thus for example in a PAW data set for oxygen where the core is 1s2, the core charge is +6 (total nuclear charge minus core electron charge). In point charge models, which are much less accurate than PAW calculations, all atomic sites are treated as ions with charges determined by their valence states. In such a case oxygen almost always would have a point charge of -2. The present variable taken together with prtefg=3 performs a full PAW computation of the electric field gradient and also a simple point charge computation. The user inputs whatever point charges he/she wishes for each atom type.

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quadmom
Mnemonics: QUADrupole MOMents
Characteristic:
Variable type: real array quadmom(ntypat)
default is 0
Relevant only when usepaw=1, and prtefg = 1 or greater.

- Array of quadrupole moments, in barns, of the nuclei. These values are used in conjunction with the electric field gradients computed with prtefg to calculate the quadrupole couplings in MHz, as well as the asymmetries. Note that the electric field gradient at a nuclear site is independent of the nuclear quadrupole moment, thus the quadrupole moment of a nucleus can be input as 0, and the option prtefg = 2 used to determine the electric field gradient at the site.

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spnorbscl
Mnemonics: SPin-ORBit SCaLing
Characteristic:
Variable type: real
default is 1.d0
Relevant only when usepaw=1, and pawspnorb = 1 (or greater).
Scaling of the spin-orbit interaction. The default values gives the first-principles value, while other values are used for the analysis of the effect of the spin-orbit interaction, but are not expected to correspond to any physical situation.
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upawu
Mnemonics: value of U for PAW+U
Characteristic: ENERGY
Variable type: real array upawu(ntypat)
default is 0
Relevant only when usepaw=1, and usepawu=1.
Gives the value of the screened coulomb interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.
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usedmatpu
Mnemonics: USE of an initial Density MATrix in Paw+U
Characteristic:
Variable type: integer parameter
default is 0
Relevant only when usepaw=1, and usepawu=1.
When usedmatpu/=0, an initial density matrix (given by dmatpawu keyword) is used and kept fixed during the first ABS(usedmatpu) SCF steps.
This starting value of the density matrix can be useful to find the correct ground state. Within LDA+U formalism, finding the minimal energy of the system is tricky; thus it is advised to test several values of the initial density matrix.
Note also that the density matrix has to respect some symmetry rules determined by the space group. If the symmetry is not respected in the input, the matrix is however automatically symmetrised.
The sign of usedmatpu has influence only when ionmov/=0 (dynamics or relaxation):
- When usedmatpu>0, the density matrix is kept constant only at first ionic step
- When usedmatpu<0, the density matrix is kept constant at each ionic step
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useexech
Mnemonics: USE of EXact EXCHange
Characteristic:
Variable type: integer parameter
default is 0
When useexexch=1, the hybrid functional PBE0 is used in PAW, inside PAW spheres only, and only for correlated orbitals given by lexexch.
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usepawu
Mnemonics: USE PAW+U (spherical part)
Characteristic:
Variable type: integer parameter
Default is 0
Relevant only when usepaw=1.

- If set to 0, the LDA+U method is not used.
- If set to 1 or 2, the LDA+U method (cf [1]) is used. The full rotationnally invariant formulation is used (see Eq. (3) of Ref [2]) for the interaction term of the energy. Two choices are allowed concerning the double counting term:

- If usepawu=1, the Full Localized Limit (FLL) (or Atomic limit) double counting is used (cf Eq. (4) of Ref.[2] or Eq. (8) of Ref[3]).
- If usepawu=2, the Around Mean Field (AMF) double counting is used (cf Eq. (7) of Ref [3]).

If LDA+U is activated (usepawu=1 or 2), the lpawu, upawu and jpawu input variables are read.
The implementation is done inside PAW augmentation regions only (cf Ref [4]). The initial density matrix can be given in the input file (see usedmatpu). The expression of the density matrix is chosen thanks to dmatpuopt. See also How_to_use_LDA+U.txt. for some informations.
References:
[1] V. I. Anisimov, J. Zaanen, and O. K. Andersen PRB 44, 943 (1991)
[2] A.I. Lichtenstein, V.I. Anisimov and J. Zaanen PRB 52, 5467 (1995)
[3] M. T. Czyzyk and G. A. Sawatzky PRB 49, 14211 (1994)
[4] O. Bengone, M. Alouani, P. Blöchl, and J. Hugel PRB 62, 16392 (2000)
Suggested acknowledgment:
- B. Amadon, F. Jollet and M. Torrent, Phys. Rev. B 77, 155104 (2008).
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