Are Molecular Exchange-correlation Functionals Transferable to Crystals

4 Are Molecular Exchange-correlation Functionals Transferable to Crystals  

The extension of HF-DFT methods to the crystalline solids encounters difficulties [371]. In molecular chemistry, very accurate thermochemical and structural data exist for a selection of simple species. These data have been effectively used to define 

7 Kohn—Sham LCAO Method for Periodic Systems 

The second difficnlty is the lack for soUds of a reference theoretical method. Post-HF techniqnes in molecnlar qnantnm chemistry can yield results with a controlled degree of accuracy. In the absence of experimental data, the results obtained with different DFT functionals conld be compared against those calculated with the reference compntational technique. Recent developments in wavefunction methods for solid-state systems (Chap. 5), GW perturbation theory [427], and quantum Monte Carlo (QMC) [428] are promising for future work, but at present they still suffer from a limited applicability. 

The latter studies conhrmed the efficiency of HF/DFT approach for solids and also use of the HSE hybrid functional. In [419] a set of 40 semiconductors was chosen based on the following criteria all considered systems were both closed shell and of simple or binary composition the majority of them have simple zincblende or rocksalt structures but also several systems with wurtzite structure were included. In addition, the availability of experimental data for lattice constants (and to a lesser extent bandgaps) was an important factor (the references to the experimental data can be found in [419]). These criteria led to the semiconductor/40 (SC/40) set of 40 soUds containing 13 group IIA-VI systems, 6 group IIB-VI systems, 17 group III-V systems, and 4 group IV systems. 

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