First principles electron-correlated calculations of linear optical absorption spectra of silicon hydrides: Si3Hn (n = 1-4).

We carried out first principles electron-correlated calculations using the Dunning's correlation-consistent polarized valence triple-zeta (cc-pVTZ) basis set to optimize the geometries and to compute linear optical absorption spectra of various silicon hydrides of the form Si3Hn, n = 1-4. The geometry optimization was performed using either unrestricted coupled-cluster singles-doubles (UCCSD) or coupled-cluster singles-doubles (CCSD) methodology. To corroborate the stability of the systems, we also carried out vibrational frequency analysis at the same level of theory employed for the geometry optimization. The descriptions of the excited states and the photoabsorption spectra were calculated using a time-dependent density functional theory (TDDFT) scheme. Isomers of Si3H, Si3H2, Si3H3, and Si3H4 systems were investigated, and a strong structure-property interconnection is observed - thus, spectral signatures of these conformers can be used for their optical detection and characterization. Our computed spectra are the first of their kind and hence, these could be explored in future experiments on these structures as a reference. The computed spectra are also constructive to identify hydrogenation induced defects in silicon thin films using optical experiments.