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MR-MCTDH[n]: Flexible Configuration Spaces and Nonadiabatic Dynamics within the MCTDH[n] Framework.
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2020-06-16 , DOI: 10.1021/acs.jctc.0c00379
Niels Kristian Madsen 1 , Mads Bøttger Hansen 1 , Graham A Worth 2 , Ove Christiansen 1
Affiliation  

Solving the time-dependent Schrödinger equation (TDSE) for large molecular systems is a complicated task due to the inherent exponential scaling of the problem. One of the most successful and versatile methods for obtaining numerically converged solutions for small to medium-sized systems is multiconfiguration time-dependent Hartree (MCTDH). In a recent publication [J. Chem. Phys.2020, 152, 084101] we introduced a hierarchy of approximations to the MCTDH method which mitigate the exponential scaling by truncating the configuration space based on a maximum excitation level w.r.t. a selected reference configuration. The MCTDH[n] methods are able to treat large systems, but the single-reference Ansatz is not optimal in cases where one (or a few) degrees of freedom are special. Examples could be double-well systems, intramolecular vibrational-energy redistribution (IVR) calculations, or nonadiabatic dynamics. In this work we introduce a multireference (MR) extension to the MCTDH[n] methods where selected higher-order excitations for the special degrees of freedom can be introduced in a simple but flexible way. The resulting MR-MCTDH[n] methods allow for, for example, treating nonadiabatic dynamics within the single-set formalism with the wave packets on each electronic surface described using the same level of approximation. Example calculations are performed on formyl fluoride (IVR), salicylaldimine (double well), and pyrazine (nonadiabatic dynamics). The results show that fast convergence is achieved by extending the configuration space in the special modes that govern the quantum dynamics.

中文翻译:

MR-MCTDH [n]:MCTDH [n]框架内的灵活配置空间和非绝热动力学。

由于问题的固有指数尺度,解决大分子系统的时间相关薛定ding方程(TDSE)是一项复杂的任务。获得中小型系统数值收敛解的最成功,最通用的方法之一是多配置时间依赖型Hartree(MCTDH)。在最近的出版物中[ J. Chem。物理 2020152,084101]我们介绍了近似的层次结构,其通过截取基于最大激励电平WRT选择的参考配置的配置空间减轻指数比例的MCTDH方法。MCTDH [ n]方法可以处理大型系统,但是在一个(或几个)自由度很特殊的情况下,单参考Ansatz并不是最佳选择。例如双井系统,分子内振动能重新分布(IVR)计算或非绝热动力学。在这项工作中,我们为MCTDH [ n ]方法引入了多参考(MR)扩展,其中可以以简单但灵活的方式引入针对特殊自由度的选定高阶激励。产生的MR-MCTDH [ n]方法允许,例如,使用相同的近似水平,用所描述的每个电子表面上的波包在单一形式形式内处理非绝热动力学。对甲酰氟(IVR),水杨醛亚胺(双孔)和吡嗪(非绝热动力学)进行示例计算。结果表明,通过控制量子动力学的特殊模式扩展构型空间,可以实现快速收敛。
更新日期:2020-07-14
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