Department of Theoretical Chemistry, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany.
J Chem Phys. 2011 Jan 7;134(1):014102. doi: 10.1063/1.3518418.
Typical (sub)system-bath quantum dynamical problems are often investigated by means of (approximate) reduced equations of motion. Wavepacket approaches to the dynamics of the whole system have gained momentum in recent years and there is hope that properly designed approximations to the wavefunction will allow one to correctly describe the subsystem evolution. The continuous-configuration time-dependent self-consistent field (CC-TDSCF) and local coherent-state approximation (LCSA) methods, for instance, use a simple Hartree product of bath single-particle-functions for each discrete variable representation (DVR) state introduced in the Hilbert space of the subsystem. Here we focus on the above two methods and replace the DVR states with the eigenstates of the subsystem Hamiltonian, i.e., we adopt an energy-local representation for the subsystem. We find that stable and semiquantitative results are obtained for a number of dissipative problems, at the same (small) computational cost of the original methods. Furthermore, we find that both methods give very similar results, thus suggesting that coherent-states are well suited to describe (local) bath states. As a whole, present results highlight the importance of the system basis-set in the selected-multiconfiguration expansion of the wavefunction. They suggest that accurate and yet computationally cheap methods may be simply obtained from CC-TDSCF/LCSA by letting the subsystem states be variationally optimized.
典型的（子）系统-浴量子动力学问题通常通过（近似）运动的约化方程来研究。近年来，整体系统的波包方法已经取得了很大的进展，并且人们希望对波函数进行适当的近似，就可以正确地描述子系统的演化。例如，连续配置时变自洽场（CC-TDSCF）和局部相干态近似（LCSA）方法，对于引入子系统 Hilbert 空间的每个离散变量表示（DVR）状态，使用浴单粒子函数的简单哈特利乘积。在这里，我们重点介绍上述两种方法，并将 DVR 状态替换为子系统哈密顿量的本征态，即，我们对子系统采用能量局部表示。我们发现，对于许多耗散问题，在与原始方法相同（小）的计算成本下，可得到稳定和半定量的结果。此外，我们发现这两种方法得出的结果非常相似，这表明相干态非常适合描述（局部）浴态。总的来说，目前的结果突出了系统基集在波函数的选择多组态展开中的重要性。它们表明，通过让子系统状态进行变分优化，就可以从 CC-TDSCF/LCSA 中获得准确且计算成本低廉的方法。
