Reactive molecular dynamics at constant pressure via non-reactive force fields: extending the Empirical Valence Bond method to the isothermal-isobaric ensemble
Ivan Scivetti, Kakali Sen, Alin M. Elena, Ilian Todorov
The Empirical Valence Bond (EVB) method offers a suitable framework to obtain reactive potentials through the coupling of non-reactive force fields. However, most of the implemented functional forms for the coupling terms depend on complex spatial coordinates, which precludes the computation of the stress tensor for condensed phase systems and prevents the possibility to carry out EVB molecular dynamics in the isothermal-isobaric (NPT) ensemble. In this work, we make use of coupling terms that depend on the energy gaps, defined as the energy differences between the participating non-reactive force fields, and derive an expression for the EVB stress tensor suitable for computations. Implementation of this new methodology is tested for a model of a single reactive malonaldehyde solvated in non-reactive water. Computed densities and classical probability distributions in the NPT ensemble reveals a negligible role of the reactive potential in the limit of low concentrated solutions, thus corroborating the validity of standard approximations customarily adopted for EVB simulations.
Self-learning hybrid Monte Carlo method for isothermal-isobaric ensemble: Application to liquid silica
自学习混合蒙特卡罗（SLHMC）是一种基于密度泛函理论的第一性原理模拟方法，它允许在势能面上精确地产生系综。统计采样可以在机器学习潜力的智能尝试移动的帮助下加速。在第一份报告（Nagai，{ \it et al}. Phys.Rev.B102，041124（R）（2020）），SLHMC方法被引入用于典型采样的最简单情况。我们在这里扩展这个想法等温等压合奏，使软材料和液体的体积波动大的一般应用。作为示范，等温等压SLHMC方法被用来研究在接近熔点的温度下的液体二氧化硅的振动结构，其中缓慢的扩散运动是超出了第一原理分子动力学的时间尺度。结果发现，从第一性原理计算的静态结构因子与高能X射线数据吻合得很好。
On the properties of a single OPLS-UA model curcumin molecule in water, methanol and dimethyl sulfoxide. Molecular dynamics computer simulation results
Structural, Electronic, and Dynamical Properties of Liquid Water by ab initio Molecular Dynamics based on SCAN Functional within the Canonical Ensemble
采用SCAN元-GGA泛函近似，对正则系综中的液态水进行了从头算分子动力学（AIMD）模拟，并与GGA水平的PBE泛函和包含PBE泛函的Tkatchenko-Scheffler van der Waals（vdW）色散修正的结果进行了系统的比较.我们分析了液态水的各种性质，包括径向分布函数，氧-氧-氧三重态角分布，四面体，氢键，扩散系数，环统计，态密度，带隙和偶极矩。我们发现，扫描功能通常是更准确的比其他两个功能的液态水，不仅捕获的中程VDW相互作用，但也减轻了PBE模拟中规定的过于强大的氢键。我们还比较了基于扫描的AIMD模拟的结果在典型的等温等压合奏。我们的研究结果表明，SCAN提供了一个可靠的描述大多数结构，电子和动力学性质的液态水。
Fast Ewald Summation with Prolates for Charged Systems in the NPT Ensemble
Center for Computational Mathematics, Flatiron Institute（西蒙斯基金会平顿研究所计算数学中心）；School of Mathematical Sciences, Shanghai Jiao Tong University（上海交通大学数学科学学院）
