An evaluation of correlation-consistent basis sets in calculating the structure and energetics of (H3Si)2O, H3SiOH, and H3SiO−

Abstract

We studied the structure of disiloxane (H3Si–O–SiH3), silanol (H3Si–OH), and the silanol anion (H3Si–O−) with ab initio molecular orbital theory and the correlation consistent polarized basis sets of Dunning and co-workers. We present results for the correlation consistent polarized valence double zeta (cc-pVDZ), triple zeta (cc-pVTZ), and quadruple zeta [cc-pVQZ(-g)] basis sets. Optimized geometries and energies are given at both the restricted Hartree–Fock (RHF) level and with the inclusion of electron correlation by second order Mo/ller–Plesset perturbation theory (MP2). The correlation consistent basis sets provide a systematic expansion of the orbital basis set, with each set of additional functions adding a similar contribution to the correlation energy. We find that the calculated molecular properties show exponential convergence with increasing basis set size. These calculations answer long-standing questions regarding the structure and barrier to linearization of disiloxane. Results at the highest level of theory [MP2/cc-pVQZ(-g)] for disiloxane gave a Si–O–Si bond angle of 147.0°, a Si–O bond length of 1.641 Å, and a barrier to linearization of 0.4 kcal/mol. All of these values are in excellent agreement with experimental results. Similar calculations for silanol gave a Si–O bond length of 1.655 Å, an O–H bond of 0.955 Å, and a Si–O–H angle of 117.9°. The MP2/cc-pVQZ(-g) deprotonation energy (ΔE0) for silanol, calculated as the energy difference between silanol and its anion, is −366.6 kcal/mol. The effects of electron correlation at the MP4 level are studied in all three molecules using the cc-pVDZ and cc-pVTZ basis sets.