Thermal fluctuations, localization, and self-trapping in a polar crystal: Combined shell-model molecular dynamics and quantum chemical approach

被引:17
作者
Gavartin, JL [1 ]
Shluger, AL [1 ]
机构
[1] UCL, Dept Phys & Astron, London WC1E 6BT, England
来源
PHYSICAL REVIEW B | 2001年 / 64卷 / 24期
关键词
D O I
10.1103/PhysRevB.64.245111
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
We study the effects of thermal disorder on the electronic structure of crystalline MgO using a combination of shell model molecular dynamics (MD),semiempirical Hartree-Fock (HF), and ab initio plane-wave density-functional (DFT) calculations. Using the atomic configurations generated by MD, we calculate by the HF method the probability distributions for the on site electrostatic potential and effective ionic charge, as well as electronic densities of states at the temperatures of 100, 300, and 500 K. We find the distribution for the on-site potential to be Gaussian, with a variance proportional to the temperature, while the ionic charge distribution is distinctly non-Gaussian. The potential and charge fluctuations contributing most to the electronic states in the valence-band tail are shown to have a structural pattern statistically similar:to the one- and two-center small hole polarons. The HF calculations of the electronic excited states of thermally disordered MgO revealed a strong one-center localization of both electrons and holes at these sites. In contrast, DFT calculations of the same systems predicted a very weak localization or no localization of the exciton. We argue that both techniques lead to unsatisfactory conclusions in that the HF method overestimates the localization effect, and the DFT method underestimates it.
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页数:13
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