Fedorov Dmitry A, Otten Matthew J, Gray Stephen K, Alexeev Yuri
Oak Ridge Associated Universities, 100 Orau Way, Oak Ridge, Tennessee 37830, USA.
Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, USA.
J Chem Phys. 2021 Apr 28;154(16):164103. doi: 10.1063/5.0046930.
Ab initio molecular dynamics (AIMD) is a valuable technique for studying molecules and materials at finite temperatures where the nuclei evolve on potential energy surfaces obtained from accurate electronic structure calculations. In this work, we present an approach to running AIMD simulations on noisy intermediate-scale quantum (NISQ)-era quantum computers. The electronic energies are calculated on a quantum computer using the variational quantum eigensolver (VQE) method. Algorithms for computation of analytical gradients entirely on a quantum computer require quantum fault-tolerant hardware, which is beyond NISQ-era. Therefore, we compute the energy gradients numerically using finite differences, the Hellmann-Feynman theorem, and a correlated sampling technique. This method only requires additional classical calculations of electron integrals for each degree of freedom without any additional computations on a quantum computer beyond the initial VQE run. As a proof of concept, AIMD simulations are demonstrated for the H molecule on IBM quantum devices. In addition, we demonstrate the validity of the method for larger molecules using full configuration interaction wave functions. As quantum hardware and noise mitigation techniques continue to improve, the method can be utilized for studying larger molecular systems.
从头算分子动力学（AIMD）是一种在有限温度下研究分子和材料的重要技术，其中原子核在由精确电子结构计算得到的势能面上演化。在这项工作中，我们提出了一种在噪声中等规模量子（NISQ）时代量子计算机上运行AIMD模拟的方法。电子能量使用变分量子本征求解器（VQE）方法在量子计算机上进行计算。完全在量子计算机上计算解析梯度的算法需要量子容错硬件，这超出了NISQ时代的能力。因此，我们使用有限差分、Hellmann-Feynman定理和相关采样技术对能量梯度进行数值计算。该方法仅需要对每个自由度进行额外的电子积分经典计算，除了初始的VQE运行外，无需在量子计算机上进行任何额外计算。作为概念验证，在IBM量子设备上对H分子进行了AIMD模拟。此外，我们使用完全组态相互作用波函数证明了该方法对更大分子的有效性。随着量子硬件和噪声缓解技术的不断改进，该方法可用于研究更大的分子系统。
