John M. McKelvey

On symmetry dilemmas in ab initio SCF studies of allyl radical and ethylene

Abstract The Thouless instability conditions of the allyl radical have been investigated at the ab initio level using minimal and extended AO basis sets. The main source of RHF-instability is found in its pi-orbital system, but there is tendency for the resulting symmetry dilemma to disappear when approaching the Hartree-Fock limit. An analogous behavior is noted for the UHF solutions of ethylene.

“Proj”: A program for calculating the electron projection function

Abstract The equations and program strategy of the program “PROJ”, which evaluates the electron projection function, P(x,z), is described. Separation of coordinates is shown to lead to greater computational efficiency and a quantitative numerical integration scheme. The scheme permits precise assignment of electronic charges to defined atoms and bonding regions.

The rotational barrier in dimethyl acetylene and related molecules

Abstract The rotational barriers in dimethyl acetylene (CH 3 CCCH 3 ), diamino acetylene (H 2 NCCNH 2 ), dihydroxy acetylene (HOCCOH), methyl trifluoro methyl acetylene (CF 3 CCCH 3 ), silyl methyl acetylene (SiH 3 CCH 3 ), propene, cis and trans 2-butene and ethane were studied by ab initio molecular orbital methods using various basis sets. The eclipsed structure for dimethyl acetylene and its CF 3 and SiH 3 analogs was found to be the most stable, as has been inferred from experimental work, and the barrier height for these compounds has been predicted. The barriers in the OH and NH 2 substituted acetylenes, propene, butene and ethane were studied in order to more clearly understand the important influences in determining the barrier mechanism; specifically, the delocalized molecular orbital and Pauling VB model have been compared.

A new integral labeling technique for Gaussian-70

Abstract A new integral labeling technique is suggested for the important program GAUSSIAN-70 that greatly increases the number of basic functions that can be handled and that facilitates incorporation of MERGE, DELETE, MOVE and ADD options.