玻色子路径积分分子动力学的周期性边界条件

Correlation-Driven Phenomena in Periodic Molecular Systems from Variational Two-electron Reduced Density Matrix Theory

Correlation-driven phenomena in molecular periodic systems are challenging to predict computationally not only because such systems are periodically infinite but also because they are typically strongly correlated. Here we generalize the variational two-electron reduced density matrix (2-RDM) theory to compute the energies and properties of strongly correlated periodic systems. The 2-RDM of the unit cell is directly computed subject to necessary $N$-representability conditions such that the unit-cell 2-RDM represents at least one $N$-electron density matrix. Two canonical but non-trivial syste…

使用收缩量子本征求解器对玻色子进行量子模拟

Quantum Simulation of Bosons with the Contracted Quantum Eigensolver

本文将CQE推广并编码至多玻色子系统，用于模拟含成对二次排斥耦合的N个谐振子，验证其在噪声下仍可准确收敛地模拟分子振动等过程。

GPU4PySCF中针对周期性体系的精确QM/MM分子动力学及其在酶催化中的应用

Accurate QM/MM Molecular Dynamics for Periodic Systems in \textsc{GPU4PySCF} with Applications to Enzyme Catalysis

本文在GPU4PySCF中实现了面向周期性体系的精确QM/MM分子动力学方法，结合分布式多极静电和赝键边界处理，并应用于分支酸变位酶催化动力学研究，揭示了速率对量子方法、区域选择和蛋白构象的敏感性。

REANN: A PyTorch-based End-to-End Multi-functional Deep Neural Network Package for Molecular, Reactive and Periodic Systems

In this work, we present a general purpose deep neural network package for representing energies, forces, dipole moments, and polarizabilities of atomistic systems. This so-called recursively embedded atom neural network model takes both advantages of the physically inspired atomic descriptor based neural networks and the message-passing based neural networks. Implemented in the PyTorch framework, the training process is parallelized on both CPU and GPU with high efficiency and low memory, in which all hyperparameters can be optimized automatically. We demonstrate the state-of-the-art accuracy…

The virial theorem with periodic boundary conditions

The virial theorem relates averages of kinetic energy and forces in confined systems. It is widely used to relate stresses in molecular simulation as measured at a boundary and in the interior of a system. In periodic systems, the theorem must be modified in order to produce useful results. We formulate the theorem so that it is valid for both confined and for periodic systems. We cross-check our formulation in a study of a small system using both Monte Carlo and molecular dynamics simulations.

Binding energies of molecular solids from fragment and periodic approaches

We calculate binding energies of four molecular solids using the Hartree-Fock (HF) and second-order Møller-Plesset perturbation theory (MP2). We obtain the energies within many-body expansion (MBE) as well as using periodic boundary conditions (PBC) to compare both approaches. The systems we study are methane, carbon dioxide, ammonia, and methanol. We use tight convergence settings to obtain the binding energies with a high precision, we estimate the uncertainties to be only few tenths of percent. We discuss several issues that affect the quality of the results and which need to be considered …

Molecular dynamics simulation of UO2 nanocrystals melting under isolated and periodic boundary conditions

Melting of uranium dioxide (UO2) nanocrystals has been studied by molecular dynamics (MD) simulation. Ten recent and widely used sets of pair potentials were assessed in the rigid ion approximation. Both isolated (in vacuum) and periodic boundary conditions (PBC) were explored. Using barostat under PBC the pressure dependences of melting point were obtained. These curves intersected zero near -20 GPa, saturated near 25 GPa and increased nonlinearly in between. Using simulation of surface under isolated boundary conditions (IBC) recommended melting temperature and density jump were successfully…

Periodic Subsystem Density-Functional Theory

By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem DFT has recently emerged as a powerful tool for reducing the computational scaling of Kohn--Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extening FDE to treat subsystems of molecular and periodic character. This goal…

Analog quantum simulation of chemical dynamics

Ultrafast chemical reactions are difficult to simulate because they involve entangled, many-body wavefunctions whose computational complexity grows rapidly with molecular size. In photochemistry, the breakdown of the Born-Oppenheimer approximation further complicates the problem by entangling nuclear and electronic degrees of freedom. Here, we show that analog quantum simulators can efficiently simulate molecular dynamics using commonly available bosonic modes to represent molecular vibrations. Our approach can be implemented in any device with a qudit controllably coupled to bosonic oscillato…

Properties of modified periodic one-dimensional hopping model

One-dimensional hopping model is useful to describe the motion of microscopic particle in thermal noise environment, such as motor proteins. Recent experiments about the new generation of light-driven rotary molecular motors found that, the motor in state i can jump forward to state i+1 or i+2, or backward to state i-1 or i-2 directly. In this paper, such modified periodic one-dimensional hopping model of arbitrary period N is studied mathematically. The mean velocity, effective diffusion constant, and mean dwell time in one single cycle are obtained. Corresponding results are illustrated and …

Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates

We study the photodissociation chemistry of a quantum degenerate gas of bosonic triatomic $ABC$ molecules, assuming two open rearrangement channels ($AB+C$ or $A+BC$). The equations of motion are equivalent to those of a parametric multimode laser, resulting in an exponential buildup of macroscopic mode populations. By exponentially amplifying a small differential in the single-particle rate-coefficients, Bose stimulation leads to a nearly complete selectivity of the collective $N$-body process, indicating a novel type of ultra-selective quantum degenerate chemistry.

Path Integral Molecular Dynamics for Fermions: Alleviating the Sign Problem with the Bogoliubov Inequality

We present a method for performing path integral molecular dynamics (PIMD) simulations for fermions and address its sign problem. PIMD simulations are widely used for studying many-body quantum systems at thermal equilibrium. However, they assume that the particles are distinguishable and neglect bosonic and fermionic exchange effects. Interacting fermions play a key role in many chemical and physical systems, such as electrons in quantum dots and ultracold trapped atoms. A direct sampling of the fermionic partition function is impossible using PIMD since its integrand is not positive definite…

周期性分子链中光学声子输运的最大传播速度与切伦科夫效应

Maximum propagation speed and Cherenkov effect in optical phonon transport through periodic molecular chains

研究周期性分子链中光学声子的弹道输运，基于声子发射/吸收的能量与动量守恒及寿命数值计算，提出群速度低于声速可抑制退相干，否则发生类切伦科夫声子发射。