Ultrasoft pseudo-potentials

The wave functions are expended in a plane wave basis set, and the effective potential of ions is described by ultrasoft pseudo potential. The generalized gradient approximation (GGA)-PW91, and local gradient-corrected exchange-correlation functional (LDA)-CAPZ are used for the exchange-correlation functional. 

Kageshima and Shiraishi directly calculated the momentum matrix elements from the wave functions at the T point, with the ultrasoft pseudo-potential method including a core-repair term [14], Their result shows that the momentum matrix elements of ZB and WZ GaN are almost the same and about 40% smaller than that of ZB GaAs. This trend is consistent with the result of Suzuki et al although the absolute values are about 30% smaller. Experimentally, the momentum matrix element was indirectly deduced from a fit to photoluminescence (PL) spectra and optical absorption by Im et al [15], Fanciulli et al measured the g-value by electron spin resonance (ESR) and indirectly determined it with the k.p model [16], The agreement between theoretical and experimental results is fairly good. 

Much lower cutoffs can be achieved with ultrasoft pseudo-potentials, relaxing the norm-conservation condition [163-167]. An augmentation charge... 

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