The study of structure characteristics of GeTe and GeSe molecules under the external electric field

Equilibrium structures of the GeTe and GeSe ground state molecules are obtained by employing the local spin density approximation method with 6-311++G** basis sets for Ge and SDB-cc-pVTZ for Te and Se. Also obtained are the equilibrium geometry, the highest occupied molecular orbital(HOMO) energy level, the lowest unoccupied molecular orbital(LUMO)energy level, the energy gap, the harmonic frequency and the infrared intensity of GeTe and GeSe ground state molecules under different electric fields. On the basis of the above calculation, the excited states of GeTe and GeSe molecules under different electric fields are also investigated by using the single-excitation configuration interaction-local spin density approximation method. The results show that the equilibrium internuclear distance and the intensity of infrared are found to increase, but the total energy and harmonic frequency are proved to decrease with the increase of positive direction electric field. The HOMO energy EH of GeTe molecule is higher than that of GeSe molecule under electric fields ranging from 0 to 2.05691010 V m-1. For GeTe and GeSe molecules, their difference in EH gradually increases with the increase of positive direction electric field. The LUMO energy EL of GeTe molecule is lower than that of GeSe molecule, and their LUMO energies are found to increase with the increase of positive direction electric field. The energy gap of GeTe is low than that of GeSe, and their energy gaps always decrease with the increase the negative direction electric field. The magnitude and the direction of the external electric field have important effects on excitation energy, oscillator strength and wavelength.