Polyak Iakov, Allan Charlotte S M, Worth Graham A
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
J Chem Phys. 2015 Aug 28;143(8):084121. doi: 10.1063/1.4929478.
We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation.
我们在此确凿地证明，变分多组态高斯（vMCG）方法对于多维隧穿问题收敛到基于网格的全量子动力学多组态含时 Hartree 结果，以水杨醛亚胺中的分子内质子转移作为模型体系。13 维模型势能面由使用 6 - 31G*基组的 Hartree - Fock 能量获得，并且沿跃迁模式的通量算符的期望值被用作基准特征。除了展示 vMCG 方法在使用局部谐波近似和适量基函数的模型表面上具有出色的收敛性之外，我们还表明 vMCG 的直接动力学版本也表现得非常好，通常需要相同数量的高斯函数来收敛，并且如果在精确拟合的表面上获得精确结果，它也会收敛到精确结果。最后，我们有一个重要的发现，即必须非常谨慎地选择高斯基函数的宽度，以便在使用固定宽度近似时获得准确的结果。
