This program performs *a posteriori*

    A) Bond order and valence analysis and

    B) "Chemical Energy Component Analysis" (CECA)

of the ab initio SCF wave functions (RHF or UHF) produced by the
widely used "Gaussian" system (G92, G94, G98).
 

Bond order and valence indices represent LCAO counterparts of the
respective classical chemical parameters (I. Mayer, Chem. Phys. Lett.
97, 270 1983...) while "CECA" is a new tool permitting 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 (I. Mayer, CPL 332, 381, 2000); three-
and four-center effects are compressed to one- and two-center ones by
performing appropriate projections.
 

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 "apost".

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
APOST 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 "APOST" 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.
 
 

Cite this program as:

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I. Mayer and A. Hamza, Program "APOST", Version 1.07
(Chemical Research Center, Hungarian Academy of Sciences),
Budapest, 2000-2004.
 
 

Limitations:

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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.