Begušić Tomislav, Cordova Manuel, Vaníček Jiří
Laboratory of Theoretical Physical Chemistry, Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
J Chem Phys. 2019 Apr 21;150(15):154117. doi: 10.1063/1.5090122.
To alleviate the computational cost associated with on-the-fly ab initio semiclassical calculations of molecular spectra, we propose the single-Hessian thawed Gaussian approximation in which the Hessian of the potential energy at all points along an anharmonic classical trajectory is approximated by a constant matrix. The spectra obtained with this approximation are compared with the exact quantum spectra of a one-dimensional Morse potential and with the experimental spectra of ammonia and quinquethiophene. In all cases, the single-Hessian version performs almost as well as the much more expensive on-the-fly ab initio thawed Gaussian approximation and significantly better than the global harmonic schemes. Remarkably, unlike the thawed Gaussian approximation, the proposed method conserves energy exactly, despite the time dependence of the corresponding effective Hamiltonian, and, in addition, can be mapped to a higher-dimensional time-independent classical Hamiltonian system. We also provide a detailed comparison with several related approximations used for accelerating prefactor calculations in semiclassical simulations.
为了减轻与分子光谱的即时从头算半经典计算相关的计算成本，我们提出了单海森矩阵解冻高斯近似，其中沿非谐经典轨迹所有点处的势能海森矩阵由一个常数矩阵近似。用这种近似得到的光谱与一维莫尔斯势的精确量子光谱以及氨和五噻吩的实验光谱进行了比较。在所有情况下，单海森矩阵版本的表现几乎与成本高得多的即时从头算解冻高斯近似一样好，并且明显优于全局谐波方案。值得注意的是，与解冻高斯近似不同，尽管相应有效哈密顿量具有时间依赖性，所提出的方法仍能精确守恒能量，此外，还可以映射到一个更高维的与时间无关的经典哈密顿系统。我们还与用于加速半经典模拟中预因子计算的几种相关近似进行了详细比较。
