Ab initio calculations on the effect of polarization functions on disiloxane

Abstract

The effect of polarization functions for ab initio molecular orbital calculations at the 3-21G* level has been studied for disiloxane. Calculated molecular geometry, dipole moment, and the linearization barrier variation were analyzed for different uncontracted polarization functions. It was concluded that variation of the polarization function on oxygen has only a minor influence on the molecular properties of disiloxane, but its presence is required to obtain a bent geometry for the disiloxane bond. The calculated molecular properties of disiloxane are greatly influenced when the polarization function on silicon is varied. Two different values (0.3 and 0.9) for the exponent of the silicon polarization function provide results comparable to the experimental values for disiloxane. The only significant differences between the results obtained from ab initio calculations using the two polarization functions are in net atomic charges. The uncontracted polarization function of silicon with a value of 0.3 for its exponent is transferable to other organosilicon compounds. Calculated molecular geometries of flexible or rigid structures are in very good agreement with the experimental values.

Ab initio calculations on some transition metal heptoxides by using effective core potentials

“…Steric effects were claimed to be enough to explain the large Si-O-Si angle in disiloxane (H 3 Si-O-SiH 3 ) [32], for which no (p-d)p bonding was observed. However, in the case of the transition metal heptoxides, the explanation of the observed trends based on steric effects alone is not fully satisfactory.…”

“…The need for a polarization function to reproduce a bent arrangement around the X-O-X moiety has already been observed for the disiloxanes and silicates [32,33], and resembles the requirement of such a function on the nitrogen atom in order to describe the pyramidal geometry of amines [34,35].…”

A gas-phase electron diffraction and quantum chemical investigation of the molecular structure of 1-bromosilacyclobutane

“…Accordingly, the addition of polarization functions (on heavy atoms in particular) is necessary to properly describe the charge redistribution produced by the bonded atoms. In this regard Grigoras and Lane [50] have pointed out that the polarization functions on silicon leads to a variation of the net atomic charge on silicon and depending on the exponent of the polarizations function the silicon atom becomes more or less highly positive.…”

Renewed focus on the small temperature change of smectic layer spacing in ferroelectric and antiferroelectric LCs

“…When an applied electric field induces the electrostatic polarisation, biaxiality arises in the molecular orientational ordering and the small change of excluded volume or molecular packing occurs. These may cause a change in the molecular conformation or a change in the core part tilt angle β c because the LC molecule possesses flexibility, especially in the siloxane substituent part [25,36,37]; hP 2 i app and hP 4 i app may considerably be affected by this molecular flexibility. According to Equation (8), the plausible assumption that same assumption gave β c ¼ 26 in field-induced SmC Ã as explained above.…”