Reduced-cost supercell approach for computing accurate phonon density of states in organic crystals
Reduced-cost supercell approach for computing accurate phonon density of states in organic crystals
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DOI：
10.1063/5.0032649
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发表时间：
2020-12-14
影响因子：
4.4
通讯作者：
Beran, Gregory J. O.
中科院分区：
文献类型：
--
作者：
Cook, Cameron;Beran, Gregory J. O.
声子对有机晶体结构和热化学性质的贡献可能是显着的，但是由于需要大型超晶胞，使用晶格动力学和周期密度泛函理论（DFT）计算良好收敛的声子态密度通常在计算上是昂贵的。使用半经验方法，如密度泛函紧束缚（DFTB）而不是DFT，可以显着降低计算成本，尽管精度明显降低。这项工作提出了通过一个相对便宜的DFTB超原胞处理的声子色散，然后通过转移个别的声子模式，根据DFT和DFTB声子频率之间的差异在伽玛点校正近似的声子态密度。然后在DFT水平上从弹性常数计算声学模式。在几个小分子晶体的测试情况下，这种组合的方法再现DFT热化学与kJ/mol的精度和1-2个数量级的计算工作量少。最后，应用该方法计算了草酰二肼五种晶型之间的自由能差。由AIP Publishing授权出版。
Phonon contributions to organic crystal structures and thermochemical properties can be significant, but computing a well-converged phonon density of states with lattice dynamics and periodic density functional theory (DFT) is often computationally expensive due to the need for large supercells. Using semi-empirical methods like density functional tight binding (DFTB) instead of DFT can reduce the computational costs dramatically, albeit with noticeable reductions in accuracy. This work proposes approximating the phonon density of states via a relatively inexpensive DFTB supercell treatment of the phonon dispersion that is then corrected by shifting the individual phonon modes according to the difference between the DFT and DFTB phonon frequencies at the Gamma-point. The acoustic modes are then computed at the DFT level from the elastic constants. In several small-molecule crystal test cases, this combined approach reproduces DFT thermochemistry with kJ/mol accuracy and 1-2 orders of magnitude less computational effort. Finally, this approach is applied to computing the free energy differences between the five crystal polymorphs of oxalyl dihydrazide. Published under license by AIP Publishing.