We describe a method to run simulations of ground or excited state dynamics under extremely high pressures. The method is based on the introduction of a fictitious ideal gas that exerts the required pressure on a molecular sample and is therefore called XP-GAS (eXtreme Pressure by Gas Atoms in a Sphere). The algorithm is most suitable for approximately spherical clusters of molecules described by quantum chemistry methods, Molecular Mechanics or mixed QM/MM approaches. We compare the results obtained by the algorithm here presented and by the XP-PCM approach, based on a continuum description of the environment. As a test case, we study the conformational dynamics of 1,3-butadiene either as an isolated molecule (“naked” butadiene) or embedded in a cluster of argon atoms, under pressures up to 15 GPa. Overall, our results show that the XP-GAS QM/MM simulation method is in good agreement with the XP-PCM QM/Continuum model (Cammi model) in describing the effect of the pressure on static properties as the equilibrium geometry of butadiene in the ground state. Furthermore, the comparison of XP-GAS simulations with naked butadiene and butadiene in argon shows the importance, for XP-GAS and related methods, of a realistic representation of the medium in modelling pressure effects.

中文翻译：

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一种用于极高压分子动力学模拟的算法


我们描述了一种在极高压力下运行基态或激发态动力学仿真的方法。该方法基于引入一种虚构的理想气体，该气体对分子样品施加所需的压力，因此称为 XP-GAS（球体中气体原子的极端压力）。该算法最适合由量子化学方法、分子力学或混合 QM/MM 方法描述的近似球形分子簇。我们根据环境的连续体描述，比较了此处介绍的算法和 XP-PCM 方法获得的结果。作为一个测试案例，我们在高达 15 GPa 的压力下研究了 1,3-丁二烯作为孤立分子（“裸”丁二烯）或嵌入氩原子簇中的构象动力学。总体而言，我们的结果表明，XP-GAS QM/MM 模拟方法与 XP-PCM QM/Continuum 模型（Cammi 模型）在将压力对静态性能的影响描述为基态丁二烯的平衡几何形状方面具有良好的一致性。此外，XP-GAS 模拟与裸露丁二烯和氩中丁二烯的比较表明，对于 XP-GAS 和相关方法，在模拟压力效应中真实表示介质的重要性。