VRDDO

Our VRDDO approximation (variable retention of diatomic differential overlap) was inspired in part by a suggestion from solid state physics by Wilhite and Euwema (1+5) The approximation consists of neglecting all one-electron integrals (both energy and overlap) and two-electron integrals that involve basis function pairs . (1)<(). (1) whose pseudo-overlap ... 

The MODPOT/VRDDO LCA0-M0-SCF programs have been meshed in with the configuration interaction programs we use. In this Cl (71) program each configuration is a spin- and symmetry-adapted linear combination of Slater determinants in the terms of the spin-bonded functions of Boys and Reeves ( 2, 3> 7 0 as formu-... 

A careful analysis of the SCF energy decomposition for an inter-molecular interaction of A and B of various perturbation energy expressions indicate that for certain perturbation formulations there is a one-to-one correspondence between certain SCF energy decomposition terms and certain terms in the perturbation expressions. Thus one can calculate the values for the terms from energy decomposition of ab-initio or ab-initio MODPOT/VRDDO SCF wave functions and compare these to the values for the same type term resulting from the perturbation theory expressions. Care must be taken to correct for possible basis set incompleteness. 

VRDDO calculations, then the most appropriate perturbation theory expressions can be used in preliminary calculations of inter-molecular interactions for the various reactants. 

U8. Popkie, H. E., and Kaufman, Joyce J., "Molecular Calculations with the VRDDO, MODPOT and MODPOT/VRDDO Procedures. . HF, F2, HC1, CI2, Formamide, Pyrrole, Pyridine and Nitrobenzene," Int. J, Quantum Chem. Symp. Issue (1976), 10, U7 —57 ... 

Popkie, H. E., and Kaufman, Joyce J., "Molecular Calculations with the MODPOT, VRDDO and MODPOT/VRDDO Procedures. IV. 

Kaufman, Joyce J., Popkie, H. E., and Preston, H. J. T., "Molecular Calculations with the Non-Empirical Ab-Initio MODPOT, VRDDO and MODPOT/VRDDO.procedures. VII. Prototype Normal Neurotransmitters and Their Metabolites," Presented at the Sixth Canadian Conference on Theoretical Chemistry, Fredericton, N. B., Canada, June 1977 ... 

The variable retention of diatomic differential overlap (VRDDO) method of Kaufman and collaborators also uses semiorthogonalization. In addition, VRDDO uses a model potential to eliminate consideration of the inner-shell electrons. Both Kashiwaga s method and the VRDDO method approximate ab initio calculations, and neither introduces empirically based parameters. 

H. E. Popkie and J. J. Kaufman, hit. J. Quantum Chem., Quantum Biolopy Symp., 2, 279 (1975). Test of Charge-Conserving Integral Approximations for a V ariable Retention of Diatomic Differential Overlap (VRDDO) Procedure for Senti-uO Imtio Molecular Orbital Calculations on Large Molecules. 

Ab Imdo MODPOT/VRDDO/MERGE Calculations on Energetic Compounds, n. Nitroexplosives RDX and a-, and 8-HMX. P. C. Hariharan,... 

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