Ab Initio Investigation of the Electronic and Geometric Structure of Magnesium Diboride,MgB_2

摘要

Employing multireference variational(MRCI)and coupled cluster(CC)methods combined with quadruple-zeta quality correlation-consistent basis set,we have studied 36 states of the magnesium diboride(Mgb_2)molecule as well as 17 states of the experimentally unknown diatomic MgB.For all states of MgB2,we report geometries,atomization energies,and dipole moments,while for the first 5 states,potential energy profiles have been also constructed.The ground state is formally of ~1A_1 V-shaped symmetry with an atomization energy of 108.1(109)kcal/mol at the MRCI(MRCI + Davidson correction)level.The first excited state(~3B_1)is less than 1 kcal/mol above the X~1A_1 state,with the next state of linear Mg-B-B geometry(b~3SIGMA~-)located 10 kcal/mol higher.In all states,bent or linear,the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s).