Ab Initio Investigation of the Structural and Electronic Properties of the Molecules and Crystals of Tetraphenyl Derivatives of Group IVA Elements

The structural and electronic properties of molecular and crystalline X(C 6 H 5 ) 4 (X = C, Si, Ge, Sn, Pb) have been studied systematically by ab initio/DFT calculations at the level of GGA-PW91 with either a plane wave basis set and ultrasoft pseudopotentials or with a local basis set−double numerical plus polarization (DNP) and all electrons. The optimized geometrical parameters were found to be comparable to the results of X-ray crystallographic, gas-phase electron diffraction, and two reported calculations for CPh 4 and SiPh 4 molecules. In addition, the electronic and optical properties such as band structures, molecular orbitals, the energy gap between the lowest unoccupied orbital (LUMO) and the highest occupied orbital (HOMO), density of states (DOS), partial density of states (PDOS), refractive indices and absorption spectra etc can be obtained from the calculations at the optimized structures. The calculated LUMO−HOMO gap is 4.1−4.6 eV. The simulated absorption spectra of XPh 4 are similar. The effect of the central atom on the HOMO, the LUMO, and other frontier molecular orbitals is increased as the atomic number of the central atom increases. Our studies showed that the present computational methods were good approximations and cost-effective for the medium-sized molecules and could be extended to the large-sized tetrahedral chromophore molecules.