Program APEX4, Version 1.02
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I. Mayer and A. Hamza
Chemical Research Center, Hungarian Academy of Sciences
H-1515 Budapest, P.O.Box 17, Hungary
e-mails: mayer@chemres.hu, hamza@chemres.hu
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This program performs *a posteriori* analysis of the
single determinant
Hartree-Fock ab initio wave wave functions produced by the
widely used
"Gaussian" system G92, G94, G98, G03. (For DFT-type wave
functions
- actulally B3LYP - the HF-like energy of the single
determinant built
up of the Kohn-Sham orbitals can be considered.)
The analyses performed:
A) Bond order and valence analysis (I. Mayer, Chem. Phys. Lett.
97, 270
1983; addendum for open shells: Chem. Phys.
Lett. 117, 396, 1985, etc.);
B) "Chemical Energy Component Analysis" (CECA), introduced in I.
Mayer,
Chem. Phys. Lett. 332, 381, 2000. CECA permits
to express the
molecular energy -- approximately but to
a good accuracy -- as a sum of
one- and diatomic energy components, the
computation of which requires
one and two-center integrals only; three- and
four-center effects are
compressed to one- and two-center ones by
performing appropriate
projections;
C) The decomposition of the two-center energy components into
terms
of different physical origin, as defined in I.
Mayer and A. Hamza
Theor. Chem. Accounts 109, 92, 2003.
D) The "Exact Energy Decomposition" as defined in I. Mayer,
Chem. Phys.
Lett. 382, 265 (2003). It differs from CECA by
the absence of
approximations and a different treatment of
the kinetic energy
and the two-center finite basis corrections.
In fact, four different energy
decomposition matrices are computed,
two approximate and two exact. They differ in the approximate or
exact treatment of the the 3- and 4-center integrals from one
side,
and in the treatment of kinetic energy integrals and (two-center)
finite basis corrections from the other. One type of
decompositions
(the approximate CECA and the exact "CECA + 3- and 4-center
terms")
contain kinetic energy mainly in the atomic terms (and in the
finite
basis corrections) while the "CECA/T" and "exact" decomposition
contain
both one-and two-centyer kinetic energy contributions and there
is no
need in the finite basis correction terms. Only two of these
four have
been described in publications as yet: see CECA in A) and
"exact" in D)
above. The diatomic components printed are essentially those in
C).
(Plus the kinetic energy is printed).
The "approximate" and "exact" schemes become identical for
diatomics.
The CECA-type quantities are good indicators of different
interactions,
but are not on the "chemical scale": there arelarge atomic
promotions and
large (in absolute value) two-center binding components. The
CECA/T and
"exact" schemes give much more "chemical" values, but should be
used only
at the equilibrium molecular geometries.
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Installation of the program:
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The "tar" file contains all the necessary FORTRAN
source files as well
as a "Makefile", which should be appropriate
to produce the executable
by issuing the command "make" on a UNIX or Linux
system. (If necessary,
replace the call to "f77" in the Makefile by
the name of your FORTRAN
compiler.) The name of the executable generated
is "apost4".
Usage of the program:
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The only input required by the program is the
"formatted checkpoint
file" (Test.FChk) which is produced by the
Gaussian,
provided that the
FormCheck keyword is included in the Gaussian
input. In the program
APEX4 the file Test.FChk is used for input as
the FORTRAN file fort.14,
and is copied to file "Tmp" for actual processing
(file fort.15).
An alternative is to conserve the binary
checkpoint
file which is
produced during the Gaussian run (include
%chk="filename"
in the input)
and to format it by using the command "formchk"
which is a part of the
Gaussian system. The formatted checkpoint file
should then be renamed
(copied) to Test.Fchk (or to fort.14, if the
statement
"open(14,file='Test.FChk')" has been deleted
from "subroutine input".
A convenient way of using the program is to
include
it in the
script performing the Gaussian run; one should
take care of ensuring
that "APEX4" should NOT start before Gaussian
is finished. It is
desirable to delete or rename the formatted
checkpoint
file Test.FChk
after the calculation, in order to avoid its
unwanted reuse.
The program is based on our program APOST. Note that the present
program may be significantly more demanding as for computer memory
and computation time.
Cite this program as:
--------------------------
I. Mayer and A. Hamza, Program "APEX4",
Version
1.0
(Chemical Research Center, Hungarian
Academy of Sciences),
Budapest, 2004.
Limitations:
---------------
This version of the program does not perform
energy partitioning
in the case of basis orbitals of type
f (or higher). In these cases
bond order and valence analysis is still performed.
Bugs etc.
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Please report bugs,
problems etc. to either of
the e-mail addresses
above - we will try our best to help you.