|
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). |