CAS SCF/CI calculations of low-lying states and potential energy surfaces of Si 3

Abstract

Complete active space MC SCF and restricted first-order CI calculations of low-lying states of Si 3 ( 1A 1, 3B 2, 1B 2, 3B 1, 1B 1, 3A 2, 1A 2) and potential energy surfaces of the 1A 1 and 3B 2 states are calculated. MRSDCI calculations are carried out for the 1A 1 and 3A' 1(D 3h) states. The ground state of Si 3 is found to be the 1A 1 state with the 3A' 2 (equilateral triangle) state 3.6 kcal mole above the singlet state in a TZ + ld basis set. A second shallow minimum (obtuse triangle, apex angle 160°) and a barrier are found in the potential energy surface of the 3B 2 state. The equilibrium geometry of the 1A 1 state is an isosceles triangle, apex angle 80° while that of the 3B 2 ( 3A' 22) state is an equilateral triangle. The equilateral and isosceles triangular structures are more stable than the corresponding linear structures.