# ABINIT internal variables:

## List and description.

This document lists several internal variables, to which the user has no direct access through a keyword, but that are derived from the input variables at the time of their processing, and used internally. Their value is fixed for a specific dataset. They are present in the dtset array, in addition to the input variables that can be directly addressed by the user.

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 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
- Parallelisation variables, VARPAR
- Projector-Augmented Wave variables, VARPAW
- Response Function variables, VARRF
- Structural optimization variables, VARRLX
- Wannier90 interface variables, VARW90

### Content of the file : alphabetical list of internals.

A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K. kptns
L.
M. mband mgfft mgfftdg mpw
N. natpawu nfft nfftdg nelect
O.
P.
Q. qptn
R.
S.
T.
U. usepaw
V.
W.
X.
Y.
Z. ziontypat

kptns
Mnemonics: K-PoinTs re-Normalized and Shifted
Characteristic: INTERNAL
Variable type: real array kptns(3,nkpt)
If nqpt=0, or if one is doing a reponse calculation, this internal variable is derived from kpt and kptnrm: kptns(1:3,:)= kpt(1:3,:)/ kptnrm, so that it is kpt renormalized by kptnrm.
If nqpt=1 and one is not doing a ground-state calculation, this internal variable is derived from kpt,kptnrm and qptn kptns(1:3,:)= kpt(1:3,:)/ kptnrm+ qptn(1:3), so that it is kpt renormalized by kptnrm, then shifted by qptn(1:3).
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mband
Mnemonics: Maximum number of BANDs
Characteristic: INTERNAL
Variable type: integer
This internal variable deduces from nband(1:nkpt*nsppol) the maximum number of bands, over all k-points and spin-polarisation.
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mgfft
Mnemonics: Maximum of nGFFT
Characteristic: INTERNAL
Variable type: integer
This internal variable gives the maximum of ngfft(1:3).
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mgfftdg
Mnemonics: Maximum of nGFFT for the Double Grid
Characteristic: INTERNAL
Variable type: integer
This internal variable gives the maximum of ngfftdg(1:3).
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mpw
Mnemonics: Maximum number of Plane Waves
Characteristic: INTERNAL
Variable type: integer
This internal variable gives the maximum of the number of plane waves over all k-points. It is computed from ecut, and the description of the cell, provided by acell, rprim, and/or angdeg.
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natpawu
Mnemonics: Number of AToms on which PAW+U is applied
Characteristic: INTERNAL
Variable type: integer parameter
This internal variable gives the number of atoms on which LDA/GGA+U method has to be applied.
It is determined by natom, usepawu and lpawu input keywords.
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nelect
Mnemonics: Number of ELECTrons
Characteristic: INTERNAL
Variable type: real number
This internal variable gives the number of electrons per unit cell, as computed from the sum of the valence electrons related to each atom (given by the pseudopotential), that is called "zval" and the input variable charge:
nelect=zval-charge.
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nfft
Mnemonics: Number of FFT points
Characteristic: INTERNAL
Variable type: integer
If the space parallelisation is not used, this internal variable gives the number of Fast Fourier Transform points, in the grid generated by ngfft(1:3). It is simply the product of the three components of ngfft.
If the space parallelisation is used, then it becomes the number of Fast Fourier Transform points attributed to this particular processor. It is no more the above-mentioned simple product, but a number usually close to this product divided by the number of processors on which the space is shared.
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nfftdg
Mnemonics: Number of FFT points for the Double Grid
Characteristic: INTERNAL
Variable type: integer
If the space parallelisation is not used, this internal variable gives the number of Fast Fourier Transform points, in the (double) grid generated by ngfftdg(1:3). It is simply the product of the three components of ngfftdg.
(To be checked : If the space parallelisation is used, then it becomes the number of Fast Fourier Transform points attributed to this particular processor. It is no more the above-mentioned simple product, but a number usually close to this product divided by the number of processors on which the space is shared.)
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qptn
Mnemonics: Q-PoinT re-Normalized
Characteristic: INTERNAL
Variable type: real array qptn(3)
Used if nqpt=1. This internal variable is derived from qpt and qptnrm: qptn(1:3)= qpt(1:3)/ qptnrm.
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usepaw
Mnemonics: USE Projector Augmented Waves method
Characteristic: INTERNAL
Variable type: integer parameter
Default is Value is set by the pseudopotential files : either PAW or norm-conserving.
If the user wants to use the Projector Augmented Method, then usepaw must be 1. This variable is determined by the pseudopotentials files. Indeed, special PAW pseudo-projector files must be used (these are the equivalent of the pseudopotential files for the pseudopotential method). Such files are NOT yet available for the entire periodic table. Also, forces and stresses are not yet computed in the PAW method as implemented in ABINITv4.1. Other limitations are present as well, precluding the use of PAW for real production work. These limitations will be waived as time passes.
Related variables : see PAW variables,
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ziontypat
Mnemonics: Z (charge) of the IONs for the different TYPes of AToms
Characteristic:
Variable type: real array ziontypat(ntypat)
Default is Value is set by the pseudopotential files.
Charge of the pseudo-ion (=number of valence electrons that are needed to screen exactly the pseudopotential).
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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