SPECTROSCOPIC CONSTANTS OF SIH2, GEH2, SNH2, AND THEIR CATIONS AND ANIONS FROM DENSITY-FUNCTIONAL COMPUTATIONS

Local (LSD) and nonlocal (NLSD) spin density calculations using different exchange-correlation functionals have been performed to determine equilibrium geometries, harmonic vibrational frequencies (omega e) ionization potentials (IP), electron affinities (EA) dipole moments (mu), and singlet-triplet energy gaps (Delta E(ST)) of SiH2, GeH2, and SnH2. Geometrical structures as well as vibrational frequencies are in agreement with the available experimental data and compare favorably with the most sophisticated post-Hartree-Fock computations performed until now. Both computed Ips (9.15 and 9.25 eV for SiH2 and GeH2, respectively) and EA of SiH2 (1.17 eV) compare favorably with experimental data (9.17, 9.21, and 1.2 eV). Accurate values are obtained also for singlet-triplet energy gaps. We report for the first time the electron affinities of all neutral systems and the spectroscopic constants of the cations and anions. (C) 1995 John Wiley & Sons, Inc.