Simulation of Defect Processes Induced by Electronic Excitation

用量子力学从头算程序模拟了碱金属卤化物中激子的弛豫过程和碱金属卤化物（100）面上F心的弛豫过程，计算了NaCl（100）面上F心基态和激发态的二维绝热势能面，通过优化激发态构型，得到了邻近F中心的碱原子垂直和平行运动的理论解。结果表明，碱金属原子在激发态的发射存在势垒。势垒的高度和APES的基态和激发态之间的分离被发现是依赖于发射的方向。看来，发射是由非辐射跃迁从激发态到基态，这是一个热势垒应克服诱导。计算结果与实验室最近的实验结果相一致.考虑组态相互作用，研究了卤素分子离子的自陷空穴和H心的光学跃迁.在没有组态相互作用的情况下，由于卤素-卤素距离较小，H中心的sigma和pi跃迁能量均高于自陷空穴的相应跃迁能量.发现两个σ极化跃迁之间的相对大的组态相互作用会降低σ跃迁能量，而π跃迁受组态相互作用的影响很小。这一结果与本实验室最近进行的实验观察相一致。

Relaxation of an exciton in the bulk of alkali halides and of an excited F center on the (100) surface of alkali halides are simulated using an ab initio quantum mechanical computer code.The two-dimensional adiabatic potential energy surfaces (APES) of a F center on the NaCl (100) surface at the ground and excited states, for the perpendicular and parallel motion of an alkali atom neighboring the F center was obtained by optimizing the configuration at the excited state. It is shown that there is a potential barrier for the emission of the alkali atom at the excited state. The height of the barrier and the separation between the APES's for the ground state and excited state are found to be dependent on the direction of the emission. It appears that the emission is induced by the non-radiative transitions from the excited state to the ground state, for which a thermal potential barrier should be overcome. The result of the calculation is in accordance with the recent experimental results obtained in our laboratory.The optical transition of the self-trapped hole and the H center, both of which consist of the halogen molecular ion, are studied by taking the configuration interaction into account. Without the configuration interaction, both the sigma and pi transition energies of the H center is found to be higher than the corresponding transition energies of the self-trapped hole, because of the smaller halogen-halogen distance. The sigma transition energy is found to be diminished by a relatively large configuration interaction between two sigma polarized transitions, while the pi transition is affected little by the configuration interaction. The result is in accordance with the experimental observation carried out recently in our laboratory.