Electronic spectrum of GeTe : An <i>ab initio</i> based configuration interaction study

Abstract

Low-lying electronic states of GeTe within 40 000 cm^-1 of energy have been studied by using <i>ab initio</i> based configuration interaction calculations which include relativistic effective core potentials (RECP) of Ge and Te atoms. We have computed potential energy curves of 18Λ-S states which correlate with the Ge(³P_g)+ Te(³P_g) dissociation limit. In addition, curves of two highly excited 3¹Σ⁺ and 3¹II states are also computed. There are 12 bound states of the Λ-S symmetry below 40 000 cm^-1. Spectroscopic constants of these Λ-S states are reported and compared with the available experimental data. The ground state of GeTe is designated as X¹Σ⁺ which is dominated by at least two equally important configurations. The calculated r_c and ω_c values of X¹Σ⁺ are 2.395 Å and 298 cm^-1, respectively. The ground-state dissociation energy of GeTe is 3.67 eV as compared with the experimental value of 4.1 ± 0.4 eV. The

calculated transition energy of the A¹II-X¹Σ⁺ transition is found to be 26 860 cm^-1 which is somewhat smaller than the experimental value of 27 751 cm^-1. The 2¹Σ⁺ state is tentatively assigned as the E state which is observed in the E←X absorption. Potential energy curves of all 50 Ω states arising from the spin-orbit interactions amung 18 Λ-S states are also computed. We have reported 17 Ω states which are bound below 30 000 cm^-1 of energy. The ³II₂-³II₀₊ splitting is estimated to be about 2200 cm^-1. The compositions of the spinorbit CI wavefunctions of all bound Ω states at r_c are calculated. Transition probabilities of several dipole-allowed transitions are calculated from CI energies and wavefunctions. The A¹II-X¹Σ⁺ transition is found to be strong. In presence of the spin-orbit coupling, A¹II₁-X¹Σ⁺₀₊ and ³II₀₊-X¹Σ⁺₀₊ transitions are most probable. Radiative lifetimes of the upper states A¹II₁ and ³II₀₊ at the lowest vibrational level are estimated.