The ground state properties and excitation properties for the SnSe molecule under different external electric fields

Effects of electric field ranging from -0.04 to 0.04 a.u., on the equilibrium structure, mulliken atomic charges, the highest occupied molecular orbital(HOMO) energy level, the lowest unoccupied molecular orbital(LUMO) energy level, energy gap, fermi energy, harmonic frequency and infrared intensities of SnSe ground state molecule are investigated by employing density functional (B3LYP) method with SDB-cc-pVTZ for Sn atom and 6-311++G** basis sets for Se atom. The magnitude and direction of the external electric field have significant effects on these characteristics of SnSe molecule. The results show that the bond length is proved to be first decreasing, and then increasing with the increase of the external field, and the minimum value is 0.2317 nm when the field strength is equal to 0.03 a.u.; electric dipole moment is found to increase linearly with the increase of external field, but the HOMO energy EH, LUMO energy EL, energy gap Eg and fermi energy EF are proved to decrease with the increase of external field. The total energy and harmonic frequency are found to first increase, and then decrease, but the infrared intensities are proved to first decrease, and then increase. The wavelengths from ground state to the first ten excited states are found to increase, but the excited energies are decreasing with the increase of the external field. Meanwhile, the sequence of excited states for SnSe molecule can be changed, and some prohibited transition can be allowed under an external field.