Amante Gabriele, Savasta Salvatore, Saija Franz, Cassone Giuseppe
Institute for Chemical-Physical Processes, National Research Council of Italy (CNR-IPCF), 98158 Messina, Italy.
Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina, 98166 Messina, Italy.
J Chem Phys. 2025 Aug 28;163(8). doi: 10.1063/5.0283248.
The inclusion of Nuclear Quantum Effects (NQEs) in molecular dynamics simulations is increasingly recognized as essential for accurately modeling systems involving light nuclei, particularly hydrogen. Classical approaches, such as standard ab initio molecular dynamics (AIMD), are not suited to predict key quantum-mechanical phenomena such as zero-point motion and proton tunneling, which can critically influence the structural behavior. This is especially true in H-bonded systems, where the strength and directionality of interactions are highly sensitive to quantum delocalization. In this work, we investigate the impact of NQEs on liquid hydrogen fluoride (HF) at standard conditions and subjected to strong external electric fields by comparing classical nuclei AIMD and path-integral AIMD simulations. HF presents a rich H-bonding network and strong molecular dipole moments, leading to the manifestation of important NQEs even in the absence of the field. Furthermore, our results demonstrate that quantum effects significantly alter the response of bulk liquid HF to applied electric fields, leading to enhanced proton delocalizations favoring the protolysis reaction 2 HF ⇌ H2F+ + F-. Similarly to water, indeed, the inclusion of NQEs lowers by one-third the field threshold necessary for dissociating HF molecules [i.e., 0.15 V/Å (classical) vs 0.05 V/Å (quantum)] and increases proton mobility. These differences become particularly evident under moderate-to-strong field strengths, where quantum simulations predict molecular dissociation and Grotthuss diffusion processes that are either absent or underestimated in classical AIMD simulations, though the general mechanism for proton migration is unaltered by the inclusion of quantum effects.
在分子动力学模拟中纳入核量子效应（NQEs）越来越被认为是精确模拟涉及轻核（特别是氢）的系统所必需的。经典方法，如标准的从头算分子动力学（AIMD），不适用于预测诸如零点运动和质子隧穿等关键量子力学现象，而这些现象会严重影响结构行为。在氢键系统中尤其如此，其中相互作用的强度和方向性对量子离域高度敏感。在这项工作中，我们通过比较经典核AIMD和路径积分AIMD模拟，研究了NQEs在标准条件下以及在强外部电场作用下对液态氟化氢（HF）的影响。HF呈现出丰富的氢键网络和强分子偶极矩，即使在没有电场的情况下也会导致重要的NQEs表现出来。此外，我们的结果表明，量子效应显著改变了液态HF整体对施加电场的响应，导致质子离域增强，有利于质子解离反应2HF⇌H2F + + F - 。与水类似，实际上，纳入NQEs将解离HF分子所需的场阈值降低了三分之一[即0.15 V/Å（经典）对0.05 V/Å（量子）]，并增加了质子迁移率。这些差异在中等到强场强下变得尤为明显，在这种情况下，量子模拟预测了分子解离和Grotthuss扩散过程，而这些过程在经典AIMD模拟中要么不存在，要么被低估，尽管质子迁移的一般机制不会因纳入量子效应而改变。
