THEORETICAL STUDY ONHBeP-ANDHPBe-ANIONS USING MULTICONFIGURATION SECOND-ORDER PERTURBATION THEORY

Abstract

Some low-lying states of the nine-valence-electron systems HBeP-and HPBe-anions have been studied for the first time using three methods CASSCF, CASPT2 and B3LYP with the contracted atomic natural orbital (ANO) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO, CASPT2/ANO and B3LYP/cc-pVTZ levels. The potential energy curves of isomerization reactions between HBeP-and HPBe-were calculated as a function of HBeP bond angle. The ground and the first excited states of HBeP-are predicted to be X2Π and A2Σ+states, respectively. The X2Σ+and A2Π states of the linear HPBe-are both first-order saddle points because they have unique imaginary frequency. Two bent minima M1 and M2 were found along the 12A′ and 12A″ potential energy surfaces, respectively. The calculated results indicated that the ground-state HBeP-is linear, while the ground-state HPBe-is bent.