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263. SAMOS: Simulated Ab Initio Molecular Orbital
System
by B. O'Leary, Department of Chemistry, University of
Alabama, Birmingham, Alabama 35294; J. E. Eilers,
Department of Chemistry, SUNY, Brockport, New York
14420; and B. J. Duke, Department of Chemistry,
University of Lancaster, Bailrigg, Lancaster, England
This offering consists of four major programs all of
which are part of this system for accomplishing
Simulated Ab Initio Molecular Orbital (SAMO)
calculations. The four components of this system are
the following:
1. SAMOM - Method for Closed-Shell
Molecules
2. SAMOU - Method for Open-Shell
Radicals, Using the Spin Unrestricted Formalism
3. SAMOP - Method for Polymers
4. SAMOL - General Library Service
Program for the SAMO System
The detailed description of each segment follows:
1. SAMOM
This program can be used to evaluate the molecular
orbitals for the molecular ground state of closed-
shell molecules, using the SAMO technique. The
resulting wave function is a simulation of the one
that would be obtained using the usual Roothaan
LCAOMO method
The elements of the Fock matrix F are transferred
from ab initio results on smaller 'pattern'
molecules.A hybrid orbital basis set,
constructed from Gaussian orbitals, is used
throughout. The overlap matrix is evaluated
exactly.
_________
Ref.: J. Eilers and D. Whitman, J. Amer. Chem.
Soc., 95, 2067 (1973).
2. SAMOU
This program can be used to evaluate the molecular
orbitals for a particular class of open-shell
radicals using the SAMO technique and the spin-
unrestricted formalism.The resulting wave
function is a simulation of the one that would be
evaluated using the ab initio unrestricted
Hartree-Fock (UHF) method
with the different orbitals for different spins Ui
and Vj satisfying the equations
The elements of the Fock matricesand are
transform ab initio UHF results on some "pattern"
radicals and closed-shell restricted Hartree-Fock
results on other "pattern" molecules. A hybrid
orbital basis set, constructed from Gaussian
orbitals, is used throughout. The overlap matrix
S is evaluated exactly. The radical must be such
that the odd electron is essentially localised in
a distinct part of the molecule.
3. SAMOP
This program evaluates the band structure of
polymers with translational symmetry in one
dimension, using the SAMO method. This method is
an economical way of simulating the results that
would be obtained by an ab initio restricted
Hartree-Fock closed-shell LCAOMO procedure.
_________
References:
1. J. Eilers and D. Whitman, J. Amer. Chem.
Soc., 95, 2067 (1973). Method for molecules.
2. B. J. Duke and B. O'Leary, Chem. Phys. Lett.,
20, 459 (1973). Polymers.
4. SAMOL
The SAMO method depends on the transferability of
Fock matrix elements over hybrid basis orbitals in
LCAOMO ab initio wave functions. The method uses
such matrix elements for small "pattern" molecules
to simulate (by transferability) the Fock matrix
for larger molecules. Since the total number of
matrix elements to be considered can be very
large, this process of "transferring" them from
the pattern molecule should be made as automatic
as possible. This program aims to do this by
producing, from a series of libraries of Fock
elements for small molecules, the Fock element
data in a form suitable for input by the programs
SAMOM and SAMOP.
The program uses two techniques. In the first,
each matrix element for the pattern molecule is
tagged automatically with a number of identifiers.
A search for the large molecule then attempts to
find matrix elements with the tags required for
that molecule from the pattern molecule libraries.
This approach is particularly suitable for large
molecules of high symmetry which are to be
simulated from a small number of small pattern
molecules. The second technique, suitable for
large molecules of low symmetry simulated from a
larger number of pattern molecules, is simpler but
requires more thought from the user. This second
technique is programmed only to give data suitable
for SAMOM.
FORTRAN IV (IBM 360/370)
Lines of Code: 8403
Recommended Citation: B. J. Duke et al., QCPE 11, 263
(1974).
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