X-ALPHA LOCAL SPIN-DENSITY ENERGY CALCULATIONS

Possible applications of density functional theory are examined with t he intent of obtaining good-quality thermochemical information, such a s atomization energies and enthalpies of formation, The local spin den sity (LSD) approximation is used. Exchange and correlation are treated in the X alpha approach, where alpha is a variable parameter. The ten tative hypothesis is that the X alpha(LSD) method basically meets the required demands of accuracy, i.e. that the energy should be correct, if cu is properly selected. A simple recipe for obtaining alpha is sug gested by the idea that non-local exchange-correlation contributions s hould change in a more or less regular fashion when atoms join to form a molecule, i.e. in a fashion largely dictated by the number and type of bonds that involve the individual atoms. Applications presented fo r organic and inorganic systems using 6-31G* wavefunctions reveal a r easonable agreement, with a standard deviation of 4.4 kcal mol(-1), be tween calculated and experimental standard gas-phase enthalpies of for mation.