Albaugh Alex, Demerdash Omar, Head-Gordon Teresa
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, USA.
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2015 Nov 7;143(17):174104. doi: 10.1063/1.4933375.
We have adapted a hybrid extended Lagrangian self-consistent field (EL/SCF) approach, developed for time reversible Born Oppenheimer molecular dynamics for quantum electronic degrees of freedom, to the problem of classical polarization. In this context, the initial guess for the mutual induction calculation is treated by auxiliary induced dipole variables evolved via a time-reversible velocity Verlet scheme. However, we find numerical instability, which is manifested as an accumulation in the auxiliary velocity variables, that in turn results in an unacceptable increase in the number of SCF cycles to meet even loose convergence tolerances for the real induced dipoles over the course of a 1 ns trajectory of the AMOEBA14 water model. By diagnosing the numerical instability as a problem of resonances that corrupt the dynamics, we introduce a simple thermostating scheme, illustrated using Berendsen weak coupling and Nose-Hoover chain thermostats, applied to the auxiliary dipole velocities. We find that the inertial EL/SCF (iEL/SCF) method provides superior energy conservation with less stringent convergence thresholds and a correspondingly small number of SCF cycles, to reproduce all properties of the polarization model in the NVT and NVE ensembles accurately. Our iEL/SCF approach is a clear improvement over standard SCF approaches to classical mutual induction calculations and would be worth investigating for application to ab initio molecular dynamics as well.
我们采用了一种混合扩展拉格朗日自洽场（EL/SCF）方法，该方法是为量子电子自由度的时间可逆玻恩-奥本海默分子动力学而开发的，用于解决经典极化问题。在这种情况下，互感计算的初始猜测通过经由时间可逆速度Verlet方案演化的辅助感应偶极变量来处理。然而，我们发现了数值不稳定性，其表现为辅助速度变量的累积，这反过来又导致在AMOEBA14水模型的1 ns轨迹过程中，即使对于实际感应偶极采用宽松的收敛容差，自洽场（SCF）循环次数也会出现不可接受的增加。通过将数值不稳定性诊断为破坏动力学的共振问题，我们引入了一种简单的恒温方案，使用贝伦德森弱耦合和诺思-胡佛链恒温器进行说明，并应用于辅助偶极速度。我们发现，惯性EL/SCF（iEL/SCF）方法在收敛阈值不太严格的情况下提供了更好的能量守恒，并且SCF循环次数相应较少，能够准确再现NVT和NVE系综中极化模型的所有性质。我们的iEL/SCF方法相对于经典互感计算的标准SCF方法有明显改进，也值得研究应用于从头算分子动力学。
