Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
Phys Chem Chem Phys. 2012 Jun 7;14(21):7765-79. doi: 10.1039/c2cp40236j. Epub 2012 Mar 28.
A linear-scaling, embedded-fragment, second-order many-body perturbation (MP2) method with basis sets up to aug-cc-pVTZ is applied to the antiparallel structure of solid hydrogen fluoride and deuterium fluoride under 0-20 GPa of ambient pressure. The optimized structures, including the lattice parameters and molar volume, and phonon dispersion as well as phonon density of states (DOS), are determined as a function of pressure. The basis-set superposition errors are removed by the counterpoise correction. The structural parameters at 0 GPa calculated by MP2 agree accurately with the observed, making the predicted values at higher pressures a useful pilot for future experiments. The corresponding values obtained by the Hartree-Fock method have large, systematic errors. The MP2/aug-cc-pVDZ frequencies of the infrared- and Raman-active vibrations of the three-dimensional solids are in good agreement with the observed and also justify previous vibrational analyses based on one-dimensional chain models; the non-coincidence of the infrared and Raman mode pairs can be explained as factor-group (Davydov) splitting. The exceptions are one pair of modes in the librational region, for which band assignments based on a one-dimensional chain model need to be revised, as well as the five pseudo-translational modes that exist only in a three-dimensional treatment. The observed pressure dependence of Raman bands in the stretching region, which red-shift with pressure, is accounted for by theory only qualitatively, while that in the pseudo-translational region is reproduced with quantitative accuracy. The present calculation proves to be limited in explaining the complex pressure dependence of the librational modes. The hydrogen-amplitude-weighted phonon DOS at 0 GPa is much less structured than the DOS obtained from one-dimensional models and may be more realistic in view of the also broad, structureless observed inelastic neutron scattering spectra. All major observed peaks can be straightforwardly assigned to the calculated peaks in the DOS. With increasing pressure, MP2 predicts further broadening of bands and breach of the demarcation between the pseudo-translational and librational bands.
应用线性标度、内埋碎片、二阶多体微扰（MP2）方法和aug-cc-pVTZ 基组，研究了常压下反平行结构的固态氟化氢和氟化氘在 0-20 GPa 下的结构。作为压力的函数，确定了优化结构，包括晶格参数和摩尔体积、声子色散以及声子态密度（DOS）。通过对基组的叠加误差进行补偿校正，消除了基组叠加误差。MP2 计算的 0 GPa 结构参数与实验观测值准确吻合，为未来实验提供了有价值的预测值。Hartree-Fock 方法得到的相应值存在较大的系统误差。三维固态的红外和拉曼活性振动的 MP2/aug-cc-pVDZ 频率与实验观测值吻合良好，也验证了基于一维链模型的先前振动分析的合理性；红外和拉曼模式对的不重合可以解释为因子群（Davydov）分裂。 librational 区的一对模式和仅在三维处理中存在的五个赝平移模式除外，它们的频带分配需要根据一维链模型进行修正。拉伸区中随压力红移的拉曼带的观测压力依赖性仅在定性上由理论解释，而赝平移区的压力依赖性则以定量精度重现。目前的计算结果表明，它在解释 librational 模式的复杂压力依赖性方面存在局限性。0 GPa 时的氢幅度加权声子 DOS 比从一维模型得到的 DOS 结构少得多，考虑到实验中也观察到了较宽、无结构的非弹性中子散射谱，这种结构可能更现实。所有主要观测到的峰都可以直接分配到 DOS 中的计算峰上。随着压力的增加，MP2 预测带宽进一步变宽，赝平移带和 librational 带之间的分界被打破。
