误差影响势能面优化结构和振动性质
Optimized structure and vibrational properties by error affected potential energy surfaces
摘要：
精确地理论确定分子在其势能面最小值处的几何参数和相应的振动性质，对于解释振动光谱实验具有根本的重要性。量子Monte Carlo技术是有希望用于大分子的相关电子结构方法，其本质上受到能量和力计算的随机误差的影响，使得所述计算相对于其他更传统的量子化学工具更具挑战性。为了克服这个缺点，在目前的工作中，我们制定的一般问题的评价分子平衡结构，谐波频率和非谐波系数的误差影响的势能面。所提出的方法，基于一个多维的拟合过程，说明连同系统和统计误差的关键评价。我们观察到，在拟合过程中使用的力，而不是能量减少了一个数量级的振动参数的统计不确定性。基于对水分子的变分蒙特卡罗计算的初步结果表明，在这个理论水平上评估几何参数、谐波和非谐波系数的可能性具有可负担的计算成本和小的随机不确定性（几何形状<0.07%，振动性质<0.7%）。
英文摘要：
The precise theoretical determination of the geometrical parameters of molecules at the minima of their potential energy surface and of the corresponding vibrational properties are of fundamental importance for the interpretation of vibrational spectroscopy experiments. Quantum Monte Carlo techniques are correlated electronic structure methods promising for large molecules, which are intrinsically affected by stochastic errors on both energy and force calculations, making the mentioned calculations more challenging with respect to other more traditional quantum chemistry tools. To circumvent this drawback in the present work we formulate the general problem of evaluating the molecular equilibrium structures, the harmonic frequencies and the anharmonic coefficients of an error affected potential energy surface. The proposed approach, based on a multidimensional fitting procedure, is illustrated together with a critical evaluation of systematic and statistical errors. We observe that the use of forces instead of energies in the fitting procedure reduces the the statistical uncertainty of the vibrational parameters by one order of magnitude. Preliminary results based on Variational Monte Carlo calculations on the water molecule demonstrate the possibility to evaluate geometrical parameters, harmonic and anharmonic coefficients at this level of theory with an affordable computational cost and a small stochastic uncertainty (<0.07% for geometries and <0.7% for vibrational properties).
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