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\begin{center}
\large{{\underline {\bf Input for the DeFT Software Package}}} \\

\vspace{0.15in}

Alain St-Amant, August 27, 1998 \\

\end{center}

\vspace{0.50in}

The following document cover's DeFT's input options.  To better illustrate
these options, I have included a large number of input decks in the
{\bf ./examples} subdirectory.  The corresponding output files are also
included in this subdirectory so that new installations of DeFT can be
verified.

\vspace{0.10in}

I will try to keep DeFT's web page (http://www.chem.uottawa.ca/DeFT.html) up to
date with hints and updates to solve the (undoubtedly) many problems with DeFT
that will surface as others apply DeFT to systems on which I typically do not
work.

\vspace{0.10in}

Matters dealing with DeFT's installation are covered in the
{\bf ./install.tex} file.

\vspace{0.50in}

\noindent
\underline{{\em \#}}

The first lines of the input deck are reserved for a descriptive title.  You
may use as many lines as you want (or none at all) for this purpose.  However,
the first character of each of these lines must be the \# symbol.

\vspace{0.50in}

The remaining input deck is keyword-driven.  The complete list of keywords is
provided in the following description.   Note that only the first four
characters of each keyword need be supplied for the program to perform
properly.  If a keyword is not listed in the input deck, than the default
value is assumed.

\vspace{0.50in}

\noindent
\underline{{\em cartesian}}

\vspace{0.10in}

The geometry will be specified in cartesian coordinates on the subsequent
lines.  For each atom, its atomic symbol (optionally followed by a descriptive
one or two character label) and its $x$, $y$, and $z$ coordinates must be
supplied.  The last atom in the system is followed by a line simply stating
{\em end}.  If the coordinates are in \AA, the keyword {\em angstroms}
must follow {\em cartesian}.  Otherwise, the default, atomic units, is
used.

\vspace{0.30in}

\noindent
\underline{{\em zmatrix}}

\vspace{0.10in}

The geometry will be specified with the use of a z-matrix.  As with the
{\em cartesian} keyword, the default units are atomic units, which again
may be overriden by using the {\em angstroms} keyword after
{\em zmatrix}.  Again, the list of atoms is terminated by a line simply
containing {\em end}.  In z-matrix format, each atom, $i$, is listed as
follows

\[ symbol \hspace{1.00in} i1 \hspace{0.10in} ri
          \hspace{0.50in} i2 \hspace{0.10in} ai
          \hspace{0.50in} i3 \hspace{0.10in} di    \]

\noindent
where $symbol$ is the atomic symbol of the atom (again, optionally followed
by a descriptive one or two character label), $ri$ is the distance between
atoms $i$ and $i1$, $ai$ is the value of the angle $i$--$i1$--$i2$, and $di$ is
the value of the dihedral $i$--$i1$--$i2$--$i3$.  The first line need only
contain $symbol$.  The second line need only go up to $ri$, while for the
third, only up to $ai$.  Dummy atoms, assigned the atomic symbol $xx$, may be
used.

\vspace{0.30in}

\noindent
\underline{{\em charge}}

\vspace{0.10in}

The charge of the system is listed after this keyword.  For example, a cation
would require the line

\[ charge \hspace{0.15in} +1 \]

\noindent
in the input deck.  The default is an uncharged system.

Once the charge and multiplicity of the system have been defined, either
explicitly or implicitly through the default values, the program will check to
see if the two are compatible for the system in question.  The program will
terminate if they are not compatible.

\vspace{0.30in}

\noindent
\underline{{\em multiplicity}}

\vspace{0.10in}

The multiplicity of the system is listed after this keyword.  For example, a
doublet would require the line

\[ multiplicity \hspace{0.15in} 2 \]

\noindent
in the input deck.  The default is a singlet.

Once the charge and multiplicity of the system have been defined, either
explicitly or implicitly through the default values, the program will check to
see if the two are compatible for the system in question.  The program will
terminate if they are not compatible.

\vspace{0.30in}

\noindent
\underline{{\em runtype}}

\vspace{0.10in}

The nature of the calculation to be performed is listed after this keyword.
If an SCF is to be performed from scratch, include the keyword {\em start}
after the {\em runtype} keyword.  If restarting an SCF from a previous run,
replace the {\em start} keyword by {\em restart}.  If a geometry
optimization is to be performed, add {\em optimize} after the
{\em runtype} keyword.  If continuing a geometry optimization, use
{\em continue}, rather than {\em optimize}.  The {\em optimize} keword
should also be used when locating a transition state (the {\em mode} keyword
must however be used elsewhere in the input deck).  When using the
{\em start}, {\em restart}, or {\em optimize} keywords, the geometry
is taken from the input file.  When using the {\em continue} keyword, the
geometry is taken from the restart file (the last geometry of the previous
run).

When performing a vibrational analysis, the {\em vibrations} keyword should
follow the {\em runtype} keyword.  The geometry at which the vibrational
analysis is to be performed is read from the restart file of a previously
completed geometry optimization run.

When one has previously performed a calculation on a molecule, and one
subsequently wishes to generate molecular electrostatic potential fitted
charges without having to go through another SCF procedure, the
{\em mesp} keyword should follow the {\em runtype} keyword.  The geometry
at which the molecular electrostatic potential is to be evaulated is read from
the restart file of the previously completed DeFT calculation (whether it be
a geometry optimization or merely a single-point SCF calculation).

To achieve SCF, we use Stewart and Pulay's pseudodiagonalization approach
(see J. J. P. Stewart, P. Csaszar, and P. Pulay, {\em J. Comp. Chem.} {\bf 3},
227 (1982), J. J. P. Stewart, {\em Int. J. Quantum Chem.} {\bf 58}, 133
(1996), or K. Wolinski, R. Haacke, J. F. Hinton, and P. Pulay,
{\em J. Comp. Chem.} {\bf 18}, 816 (1997) for more details).  To locate
equilibrium geometries and transition states, we work in internal coordinates
(see P. Pulay and G. Fogarasi, {\em J. Chem. Phys.} {\bf 96}, 2856 (1992) or
C. Peng, P. Y. Ayala, H. B. Schlegel, and M. J. Frisch,
{\em J. Comp. Chem.} {\bf 17}, 49 (1996) for more details).  To fit the
electrostatic potential, the Merz-Kollman-Singh approach is used
(see B. H. Besler, K. M. Merz, Jr., and P. A. Kollman, {\em J. Comp. Chem.}
{\bf 11}, 431 (1990) for more details).  Finally, DeFT does not have
analytic second or third derivatives.  Therefore, vibrational analyses are
performed using Komornicki and McIver's algorithm (see A. Komornicki and
J. W. McIver, {\em J. Chem. Phys.} {\bf 90}, 2014 (1979) for more details).

The default for the {\em runtype} keyword is simply {\em start}, i.e., a
single SCF is run from scratch and no geometry optimization is performed.

\vspace{0.30in}

\noindent
\underline{{\em potential}}

\vspace{0.10in}

The nature of the functional for the exchange-correlation (XC) energy density
and potentials follows the {\em potential} keyword.  The default, {\em
local}, selects the Vosko-Wilk-Nusair (VWN) local spin density functional
(S. H. Vosko, L. Wilk, and M. Nusair, {\em Can. J. Phys.} {\bf 58}, 1200
(1980)).  A gradient-corrected functional can be selected by using the
{\em beckeperdew} keyword instead.  This approach uses Becke's
gradient-corrected exchange functional (A. D. Becke, {\em Phys. Rev. A}
{\bf 38}, 3098 (1988)) and Perdew's gradient-corrected correlation functional
(J. P. Perdew, {\em Phys. Rev. B} {\bf 33}, 8822 (1986)).

If one uses the  {\em mixbeckeperdew} keyword, SCF calculations are
performed with the VWN local spin density functional, and gradient corrections
are added perturbatively to the energy and energy gradients.  Such calculations
make use of the first and second derivatives of the self-consistent VWN
density in the formulae for the total energy and energy gradients.  An exact
energy gradient is not possible if such a perturbative approach is employed.
For more details on this perturbative approach, see A. St-Amant, W. D. Cornell,
T. A. Halgren, and P. A. Kollman, {\em J. Comp. Chem.} {\bf 16}, 1483 (1995).

\vspace{0.30in}

\noindent
\underline{{\em grid}}

\vspace{0.10in}

The quality of the grid required for the evaluation of the exchange and
correlation (XC) terms is specified after the {\em grid} keyword.  The
algorithm employed to generate the grid is that proposed by Stratmann,
Scuseria, and Frisch (R. E. Stratmann, G. E. Scuseria, and M. J. Frisch,
{\em Chem. Phys. Lett.} {\bf 257}, 213 (1996)).  The quality of any grid
depends on the number of radial points surrounding each atom and the
number of angular points associated with each such radial point.

Seven possibilities exist for the quality of the radial grid.  Each level is
assigned an integer:

\begin{center}
\begin{tabular}{cc}
\multicolumn{1}{c}{grid}             &
\multicolumn{1}{c}{\# radial points} \\ \hline
1 & 24 \\
2 & 32 \\
3 & 40 \\
4 & 48 \\
5 & 64 \\
6 & 80 \\
7 & 96 \\
\hspace{1.50in} & \hspace{1.50in} \\
\end{tabular}
\end{center}

\vspace{-0.15in}

\noindent
For the angular grid, four possibilities exist, and each is equally associated
with an integer:

\begin{center}
\begin{tabular}{cc}
\multicolumn{1}{c}{grid}              &
\multicolumn{1}{c}{\# angular points} \\ \hline
1 & 26 \\
2 & 50 \\
3 & 110 \\
4 & 194 \\
\hspace{1.50in} & \hspace{1.50in} \\
\end{tabular}
\end{center}

\vspace{-0.15in}

The {\em quality} keyword is followed by a four digit integer.  The first
digit corresponds to the quality of the radial grid used for the evaluation of
the final total energy and the energy gradient.  The second digit corresponds
to the quality of the angular grid used for the evaluation of the same.  The
third and fourth digits are associated with the qualities of the the radial and
angular grids, respectively, employed for the evaluation of the XC potential
throughout the course of the SCF procedure.  Provided one does not require an
exact energy gradient, experience has shown that a lesser quality grid can be
used for the SCF procedure.

The default grid quality is 5454.

If one is willing to live with an inexact energy gradient, experience has
shown that the 5433 grid will yield virtually identical results as the
5454 grid in most every case.  Please note that use of such a mixed quality
grid will mean inexact energy gradients (i.e., the true energy minimum and the
point at which the gradient vanishes are not exactly the same).  Also note that
the total energy calculated at each iteration in the the SCF procedure will be
different from the final total energy printed out at the end of the SCF
procedure.  The latter energy value is more precise and should be used for all
calculations of energy differences.  Also note that if a mixed quality grid
is used, it is essentially pointless to invoke the {\em weight} option to
include the calculation of point weight derivatives in the calculation of the
energy gradients as an exact energy gradient is no longer possible anyways with
the mixed quality grid.  Since the default is to calculate these point weight
derivatives, {\em weights off} should be included in the input deck (consult
the {\em weights} keyword for more details).

\vspace{0.30in}

\noindent
\underline{{\em weights}}

\vspace{0.10in}

For the calculation of the energy gradient to be as exact as possible, the
derivatives of the grid points' weights must be included in the calculation
(see B. G. Johnson, P. M. W. Gill, and J. A. Pople, {\em J. Chem. Phys.}
{\bf 98}, 5612 (1993) for more details).  However, it has been argued that
the errors generated by neglecting these weight derivatives are negligeable
(see J. Baker, J. Andzelm, A. Scheiner, and B. Delley, {\em J. Chem. Phys.}
{\bf 101}, 8894 (1994)) when a grid of suitable quality is used.  If the
user wishes to include the calculation of the grid points' weight derivatives
and get the best possible answers, the {\em on} keyword should follow the
{\em weights} keyword.  To neglect these derivatives in the calculation of
the energy gradient (and save a non-negligeable amount of CPU time), the
{\em off} keyword should follow the {\em weights} keyword.

The default for the {\em weights} keyword is {\em on}.

\vspace{0.30in}

\noindent
\underline{{\em maxiterations}}

\vspace{0.10in}

The maximum number of iterations in an SCF procedure is listed after this
keyword. The default value is 50.

\vspace{0.30in}

\noindent
\underline{{\em dconvergence}}

\vspace{0.10in}

The convergence criterion for the SCF procedure is defined after this keyword.
The default value is 0.00000001.  For an SCF procedure to be declared
converged, the change in the total energy, in atomic units, and the maximum
change in any one element of a density matrix must both be below the value
defined after {\em dconvergence}.

\vspace{0.30in}

\noindent
\underline{{\em mixing}}

\vspace{0.10in}

The mixing parameter for the SCF procedure is listed after this keyword.
For example, if one wishes to mix 40\% of the new density with 60\% of the
previous iteration's density, then one would have to include the following
line

\[ mixing \hspace{0.15in} 0.40 \]

\noindent
in the input deck.  The default value is 0.10.

If the DIIS algorithm is employed (the default), the value of this mixing
parameter essentially becomes irrelevant, and it should not be altered from
its default value.  If set too large, large oscillations in the density
matrix may arise and the DIIS option cannot be invoked properly.

\vspace{0.30in}

\noindent
\underline{{\em diis}}

\vspace{0.10in}

Pulay's DIIS scheme (P. Pulay, {\em J. Comp. Chem.} {\bf 3}, 556 (1982))
for accelerating the convergence of the SCF procedure is either turned on or
off by simply following the {\em diis} keyword with {\em on} or
{\em off}.  The default value is {\em on}.

\vspace{0.30in}

\noindent
\underline{{\em levelshift}}

\vspace{0.10in}

A non-zero value following this keyword will invoke Carbo's levelshifting
scheme (R. Carbo, {\em Chem. Phys. Lett.} {\bf 47}, 581 (1977)).  The value
specified (in eV) after the {\em levelshift} keyword will lower occupied
orbitals by this amount and raise virtual orbitals by this amount.  The
default value is 0.0, i.e., Carbo's algorithm is not active.  This can be used
when convergence is complicated by a small HOMO/LUMO gap.

The current version of DeFT does not allow for fractional occupation numbers
(in DeFT, a level is either fully occupied or completely empty).  Therefore,
when performing a calculation on a system where a set of degenerate orbitals
cannot be equally occupied (e.g., the ground state of the carbon atom), the
{\em levelshift} option must often be invoked, with a shift of roughly one or
two eV, to achieve an SCF.  It may also be necessary to reduce the convergence
criterion in these cases since, even though the energy is stable, the density
is very slowly converging.

\vspace{0.30in}

\noindent
\underline{{\em maxgeometries}}

\vspace{0.10in}

The maximum number of steps in a geometry optimization procedure is listed
after this keyword.  The default value is 30.

\vspace{0.30in}

\noindent
\underline{{\em gconvergence}}

\vspace{0.10in}

The convergence criterion for the geometry optimization is defined after this
keyword.  Four criteria are actually used to determine if the geometry has
been optimized:  the RMS value of the gradient vector's elements, the maximum
absolute value of any gradient vector element, the RMS change in the positions
of the nuclei, and the the largest change in any one nuclear position.  For a
geometry to be declared optimized, the four listed criteria must be below
0.00030, 0.00045, 0.00120, and 0.00180 atomic units, respectively.  The user
can only control the last value with the aid of the {\em gconvergence}
keyword.  The value provided after this keyword must be provided in atomic
units.  The default value is 0.00180.

\vspace{0.30in}

\noindent
\underline{{\em maxstep}}

\vspace{0.10in}

The maximum step size in a geometry optimization is defined after this keyword.
The default value, 0.30, means that the largest displacement of any one atom
cannot exceed 0.30 atomic units in any one step of the geometry optimization.

\vspace{0.30in}

\noindent
\underline{{\em bfreeze}}

\vspace{0.10in}

When performing a geometry optimization, any number of bonds (or internal
degrees of freedoms) can be frozen to the lengths initially provided in the
input deck.  This can be done regardless of whether the geometry is input
as cartesian or internal coordinates.

To freeze a bond, the {\em bfreeze} keyword is followed by the numbers
of the two atoms for which the interatomic distance is to be fixed.  For
example, to freeze the bond between the second and fourth atoms in the
molecule, the following line

\[ bfreeze \hspace{0.15in} 2 \hspace{0.15in} 4 \]

\noindent
would be added to the input deck.  One such line must be included for each
bond to be frozen.

\vspace{0.30in}

\noindent
\underline{{\em afreeze}}

\vspace{0.10in}

The {\em afreeze} keyword is analagous to the {\em bfreeze} keyword.  It
is, however, used to freeze a bond angle.

To freeze a bond angle, the {\em afreeze} keyword is followed by the numbers
of the three atoms involved in the angle to be frozen.  The second atom listed
after the {\em afreeze} keyword is the central atom of the bond angle to
be frozen.

\vspace{0.30in}

\noindent
\underline{{\em dfreeze}}

\vspace{0.10in}

The {\em dfreeze} keyword is analagous to the {\em bfreeze} keyword.  It
is, however, used to freeze a dihedral angle.

To freeze a dihedral angle, the {\em dfreeze} keyword is followed by the
numbers of the four atoms involved in the dihedral to be frozen.  The dihedral
is that angle formed by the first and fourth atoms listed when looking down
the bond formed by the second and third atoms listed after the {\em dfreeze}
keyword.

\vspace{0.30in}

\noindent
\underline{{\em ifreeze}}

\vspace{0.10in}

The {\em ifreeze} keyword is analagous to the {\em bfreeze} keyword.  It
is, however, used to freeze an improper torsion, or in other words, the angle
between a bond (between the ``end" atom and the ``apex" atom) and a plane
defined by two bonds (between each of two ``anchor" atoms and the ``apex"
atom).

To freeze an improper torsion, the {\em ifreeze} keyword is followed by the
numbers of the four atoms involved in the improper torsion to be frozen.
The first atom listed is the ``end" atom, the second and the third are the
``anchor" atoms, and the fourth is the ``apex" atom.

\vspace{0.30in}

\noindent
\underline{{\em mode}}

\vspace{0.10in}

The {\em mode} keyword is used to drive a geometry optimization uphill along
one, and only one, vibrational mode, i.e., this keyword is used when trying
to locate a transition state.  If the {\em mode} keyword is invoked, the
{\em optimize} keyword must follow the {\em runtype} keyword elsewhere in the
input deck.  The initial geometry need not possess the correct number of
negative values in its Hessian.  No initial Hessian need be supplied either.

The algorithm used in DeFT merely requires the user to define a bond,
bond angle, dihedral angle, or improper torsion that he/she feels has a
large component along the normal mode associated with the transition state's
imaginary frequency.  Only one such internal coordinate may be defined,
and many internal coordinates can lead to the same transition state.
Different internal coordinates can however lead to different transition
states.  The first uphill step in the search for a transition state is
entirely along the internal coordinate selected by the user.  All subsequent
steps uphill are along the normal mode most similar to the imaginary normal
mode of the previous geometry.  A Hessian possessing one, and only one,
negative eigenvalue is generated using Baker's algorithm (J. Baker,
{\em J. Comp. Chem.} {\bf 7}, 385 (1986)) and Bofill's updating scheme
(J. M. Bofill, {\em J. Comp. Chem.} {\bf 15}, 1 (1994)).

To drive uphill along a bond, bond angle, dihedral angle, or improper
torsion, a {\em b}, {\em a}, {\em d}, or {\em i} must, respectively, follow
the {\em mode} keyword.  The precise nature of the chosen internal
coordinate is defined with the numbers of the atoms involved, in exactly the
same fashion as with the {\em bfreeze}, {\em afreeze}, {\em dfreeze}, or
{\em ifreeze} keywords, as appropriate.

In practice, locating a transition state can be far more problematic than
locating an equilibrium geometry.  It may be necessary to reduce the maximum
step taken between any two geometries with the aid of the {\em maxstep}
keyword.  It may also be necessary to halt the transition state optimization
at some point when oscillations occur in the maximum component of the
gradient vector.  It is best to start a new run with the geometry from the
previous run where the gradient vector's elements were at their smallest.

\vspace{0.30in}

\noindent
\underline{{\em pointcharges}}

\vspace{0.10in}

This keyword is used when one wishes to create a reaction field by placing
point charges around a molecule.  The $x$, $y$, and $z$ coordinates, as well
as the actual charge of the particles, follow on subsequent lines, one line
per point charge.  As with the geometry specification, if the coordinates are
in \AA, then the {\em angstroms} keyword should follow the
{\em pointcharges} keyword.  Otherwise, the default is atomic units.
Again, as in the geometry input, the list of point charges is terminated by
a line that simply contains the keyword {\em end}.

\vspace{0.30in}

\noindent
\underline{{\em orbitals}}

\vspace{0.10in}

In DeFT, the molecular orbitals are generated by annihilation, i.e., by
exploiting the fact that the virtual and occupied orbitals cannot mix through
the Kohn-Sham, or Fock, operator (see J. J. P. Stewart, P. Csaszar, and
P. Pulay, {\em J. Comp. Chem.} {\bf 3}, 227 (1982) or J. J. P. Stewart,
{\em Int. J. Quantum Chem.} {\bf 58}, 133 (1996) for more details).  To
analyze the molecular orbitals produced by DeFT, the user has the option to
generate either the canonical Kohn-Sham orbitals (those that would have been
generated by the more conventional diagonalization approach) or the Boys
localized orbitals.  To generate the former, the {\em canonical} keyword must
follow the {\em orbitals} keyword.  To generate the latter, the {\em boys}
keyword must follow the {\em orbitals} keyword.  To generate both sets of
orbitals, the {\em both} keyword must follow the {\em orbitals} keyword.

Note that orbital energies are printed out only if the canonical orbitals are
requested.

\vspace{0.30in}

\noindent
\underline{{\em diffuse}}

\vspace{0.10in}

DeFT allows the user to use any basis set desired, provided it respects the
constraints/limitations of the software.  However, some basis sets can be
rapidly invoked with the aid of keywords.  By default, such basis sets do not
contain diffuse functions.  Diffuse functions can be added to these pre-defined
basis sets with the aid of the {\em diffuse} keyword.  To add a set of
diffuse $s$ and $p$ functions (and $d$ functions for elements beyond Ar) to
heavy (non-hydrogen) atoms, a 1 must follow the {\em diffuse} keyword.  To add,
beyond the aforementioned diffuse functions on heavy atoms, a diffuse set of
$s$ and $p$ functions to hydrogen atoms, a 2 must follow.

The default value for the {\em diffuse} keyword is 0, i.e., no diffuse
functions are added to any atom.

\vspace{0.30in}

\noindent
\underline{{\em mesp}}

\vspace{0.10in}

To generate a set of atom-centered point charges that are best able to 
reproduce a molecule's electrostatic potential at it's van der Waals surface,
the {\em mesp} keyword must be invoked.  By default, a DeFT calculation
does not perform this task.  The user has the option of using a set of default
points or a set of user supplied points on which to calculate the molecular
electrostatic potential.  For the former,

\[ mesp \;\; default \]

\noindent
must be included in the input deck, while for the latter,

\[ mesp \;\; read \]

\noindent
must be included in the input deck.  If points are to be read in from a file,
they must be in the {\bf molecule.pts} file in the same subdirectory
containing the {\bf molecule.dft} input file.  The coordinates of the points
must be given in the 3f20.12 format and must be in \AA, and not in
atomic units.  The coordinates of the points must also be consistent with
the coordinates of the atoms as defined in the input deck.

The algorithm for fitting the point charges to the electrostatic potential
evaluated over the set of default/supplied points is that of Merz, Kollman,
and Singh (see B. H. Besler, K. M. Merz, Jr., and P. A. Kollman,
{\em J. Comp. Chem.} {\bf 11}, 431 (1990)).

\vspace{0.30in}

\noindent
\underline{{\em equivalent}}

\vspace{0.10in}

When using the molecular electrostatic potential to generate a set of
atom-centered point charges, the fitting procedure employed is constrained
only in that the sum of the point charges must equal the total charge of the
system under study.

If one wishes to constrain two atoms to having the same point charges, the
{\em equivalent} keyword is followed by the numbers of the two atoms
involved.  For example, to ensure that the second and fourth atoms are
assigned the same point charges, the following line

\[ equivalent \hspace{0.15in} 2 \hspace{0.15in} 4 \]

\noindent
would be added to the input deck.  One such line must be included for each
pair of atoms to be so constrained.

The {\em equivalent} keyword can be used, in conjunction, with the
{\em neutral} keyword.  It can only be invoked when {\em runtype mesp}
is also included in the input deck, i.e., when restarting from a previously
converged SCF.

This option is useful for those wishing to generate point charges for
molecular dynamics and Monte Carlo runs where, over the course of the
simulation, a group of atoms should be equivalent.  One such possibility
is the three hydrogen atoms in a freely rotable methyl group.

\vspace{0.30in}

\noindent
\underline{{\em neutral}}

\vspace{0.10in}

When using the molecular electrostatic potential to generate a set of
atom-centered point charges, the fitting procedure employed is constrained
only in that the sum of the point charges must equal the total charge of the
system under study.

If one wishes to constrain a set of atom-centered point charges to summing
up to zero, i.e., forming a neutral fragment, the {\em neutral} keyword is
followed by the numbers of the atoms in the fragment.  For example, to ensure
that the third, fourth, fifth, and sixth atoms form a neutral fragment, the
following line

\[ neutral \hspace{0.15in} 3 \hspace{0.15in} 4
           \hspace{0.15in} 5 \hspace{0.15in} 6 \]

\noindent
would be added to the input deck.  One such line must be included for each
fragment.  Any number of atoms is permitted within a fragment.

The {\em neutral} keyword can be used, in conjunction, with the
{\em equivalent} keyword.  It can only be invoked when {\em runtype mesp}
is also included in the input deck, i.e., when restarting from a previously
converged SCF.

This option is useful for those wishing to generate point charges for
fragments that are part of a larger molecular mechanical force field.

\vspace{0.30in}

\noindent
\underline{{\em end}}

\vspace{0.10in}

The {\em end} keyword is used to indicate that all the desired options
have been invoked.  This serves as the separation between the list of
keywords and the designation of the basis sets.

\vspace{0.50in}

\noindent
\underline{{\em Specification of the Auxiliary and Orbital Basis Sets}}

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The basis sets to be used must be defined.  DeFT currently comes with one set
of default orbital basis sets and one set of default charge density fitting
bases.  Note that this version of DeFT does not employ fits to the
exchange and correlation terms.  Future versions of DeFT will reintroduce
this option in an improved form to that employed in the previous version of
DeFT.  In this version, the exchange and correlation terms are always
numerically integrated on a grid.  Even though there is only one default
set for each type of basis, the following lines must be entered at the end
of the input file:
\[ aux1a \;\;     \]

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\[ tzp/dzp        \]
The nature of these bases, i.e., how they were generated, is provided elsewhere
(see N. Godbout, D. R. Salahub, J. Andzelm, and E. Wimmer, {\em Can. J. Chem.}
{\bf 70}, 560 (1992)).  The precise values of the exponents and coefficients
are listed in the {\bf ./bases} file.

Note that diffuse functions can be added to the orbital basis sets with
the aid of the {\em diffuse} keyword.  Basis sets up to element 54, Xe, are
included in DeFT.

The user can replace the default bases with other bases.  To do so, the
user must include the new bases in the {\bf ./bases} file.  The same format
as used for the default bases should be adopted, and a unique name should be
given to each newly created basis.  These unique names must then be listed
at the end of the input deck, atom after atom, first for the auxiliary charge
density fitting bases, and then, atom after atom, for the orbital bases.  If
any one non-default basis is to be used for any one atomic center, this
approach must be taken for every atom in the input deck.  The names of the
default bases, as given in the {\bf ./bases} file, can be used for those
atomic centers that will retain their default bases.

\end{document}
