Diffusion Monte Carlo evaluation of disiloxane linearisation barrier.

Adie Tri Hanindriyo,Kenta Hongo,Tom Ichibha,Amit Kumar Singh Yadav,Ryo Maezono,Kousuke Nakano

doi:10.1039/d1cp01471d

Abstract

The disiloxane molecule is a prime example of silicate compounds containing the Si-O-Si bridge. The molecule is of significant interest within the field of quantum chemistry, owing to the difficulty in theoretically predicting its properties. Herein, the linearisation barrier of disiloxane is investigated using a fixed-node diffusion Monte Carlo (FNDMC) approach, which is one of the most reliable ab initio methods in accounting for the electronic correlation. Calculations utilizing the density functional theory (DFT) and the coupled cluster method with single and double substitutions, including noniterative triples (CCSD(T)) are carried out alongside FNDMC for comparison. It is concluded that FNDMC successfully predicts the disiloxane linearisation barrier and does not depend on the completeness of the basis-set as much as DFT or CCSD(T), thus establishing its suitability.

Highlights

The simplest molecule containing the Si–O–Si bond is disiloxane or Si2H6O
fixed-node diffusion Monte Carlo (FNDMC) results are affected by the choice of basis-set,[27,31] we note that the basis-set dependency is considerably different from that for a self-consistent-field (SCF)-based method, such as the density functional theory (DFT) and molecular orbital (MO) methods
A comparison between the MP2 and CCSD(T) geometry optimization with the cc-pVTZ basis-set is shown in the Electronic supplementary information (ESI).† With a difference of 0.5 degrees for the Si–O–Si angle between the two calculation methods at the cc-pVTZ level, and a linearization barrier difference of less than 0.001 kcal molÀ1 calculated for both geometries at MP2 and CCSD(T) level, geometry optimization at the MP2 level of theory does not seem to significantly impact the linearization barrier calculated at the CCSD(T) level

Summary

Introduction

The simplest molecule containing the Si–O–Si bond is disiloxane or Si2H6O. called disilyl ether, its structure is a single Si–O–Si bond terminated by three H atoms at each end (H3Si– O–SiH3). There have been numerous studies investigating the Si–O–Si bond,[1,2,3,4,5] owing to its importance in the modelling of silica compounds, which are the most abundant constituent of the Earth’s crust. In SCF-based approaches, the choice of the basis-set affects both the amplitude and the nodal positions of the corresponding many-body wavefunctions ( the methods do not explicitly employ a many-body wavefunction condition). The amplitude can be automatically adjusted such that its shape approaches that of the exact solution as closely as possible under a restriction with fixed nodal positions.[22,32] Its typical example is the description of electron–nucleus cusps.[33] Even without explicit inclusion of the singular

Methods

Results

Conclusion