Analytic second derivatives in restricted Hartree–Fock theory. A method for high‐spin open‐shell molecular wave functions

摘要: Theoretical methods have been developed for the analytic determination of second energy derivatives (i.e., force constants) from restricted Hartree–Fock wave functions certain types open‐shell systems. Specifically treated are systems which all electrons outside closed shells their spins parallel. Although formalism is somewhat complicated, its application once implemented, not greatly more arduous than closed‐shell theory presented in 1979 by Pople and co‐workers. Like previous procedures evaluation repulsion integrals, present method exploits Rys polynomial concept. Beyond this general framework, however, significant departures appear, these differences described. Preliminary new has to two lowest triplet states formaldehyde molecule, both equilibrium geometry harmonic vibrational frequencies evaluated.