Classical and inverted structures of SiXnH3-nLi and SiXnH3-nNa

Geometry, energetics, and dipole moments of tetrahedral-like (classical) an d inverted forms of SiXnH3-nLi and SiXnH3-nNa, where X stands for a halogen atom, are studied ab initio at HF, MP2, QCISD(T), and B3LYP levels of the theory using triple-zeta plus polarization and diffuse functions basis sets . The inverted form is found to be the most stable for all the cases where Li is present but not in ail the cases involving Na. Energy differences bet ween classical and inverted forms range from -2 to 24 kcal mol(-1). The res ults for SiH3Li agree with previous data. Agreement of the properties deter mined using this methodology with the experimental results; where available , is found very satisfactory. An analysis of the bonding in these molecules in terms of atomic charges and electron density is carried out.