Anharmonic Vibrational States of Solids from DFT Calculations. Part I: Description of the Potential Energy Surface
Anharmonic Vibrational States of Solids from DFT Calculations. Part I: Description of the Potential Energy Surface
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DOI：
10.1021/acs.jctc.9b00293
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发表时间：
2019-06-01
影响因子：
5.5
通讯作者：
Dovesi, Roberto
中科院分区：
文献类型：
--
作者：
Erba, Alessandro;Maul, Jefferson;Dovesi, Roberto
本文提出了一种计算固体非简谐振动态的方法，该方法通过振动组态相互作用（VCI）方法显式地考虑声子-声子耦合，由量子力学DFT计算得到固体非简谐振动态。Born-Oppen-heimer势能面（PES）以平衡核组态为中心，以简谐法向坐标展开为泰勒级数，截断为四阶，包含单模、双模和三模原子间力常数。的PES的非谐项的描述涉及的数值计算的高阶能量导数（立方和四次在我们的情况下）相对于核位移，并构成最计算要求的步骤中的非谐振动状态的材料的特性。第一部分是专门的PES的描述。提出了四种不同的数值方法来描述电势，所有这些方法都基于在法向坐标的基础上的PES的网格表示，其需要在每个点处评估不同的成分（能量和/或力）（即，核结构）的网格。讨论了两个分子系统（水和甲烷）和两个扩展的固体（冰XI和MgH 2）的PES的描述的各种方案的数值稳定性和相对计算效率。所有提出的算法被实施到一个发展版本的水晶程序。
A computational approach is presented to compute anharmonic vibrational states of solids from quantum-mechanical DFT calculations by taking into explicit account phonon phonon couplings via the vibrational configuration interaction (VCI) method. The Born-Oppen-heimer potential energy surface (PES) is expanded in a Taylor's series in terms of harmonic normal coordinates, centered at the equilibrium nuclear configuration, is truncated to quartic order, and contains one-mode, two-mode, and three-mode interatomic force constants. The description of the anharmonic terms of the PES involves the numerical evaluation of high-order energy derivatives (cubic and quartic in our case) with respect to nuclear displacements and constitutes the most computationally demanding step in the characterization of anharmonic vibrational states of materials. Part I is devoted to the description of the PES. Four different numerical approaches are presented for the description of the potential, all based on a grid representation of the PES in the basis of the normal coordinates, that require different ingredients (energy and/or forces) to be evaluated at each point (i.e., nuclear configuration) of the grid. The numerical stability and relative computational efficiency of the various schemes for the description of the PES are discussed on two molecular systems (water and methane) and two extended solids (Ice-XI and MgH2). All the presented algorithms are implemented into a developmental version of the CRYSTAL program.