The anharmonic frequencies of the O–H and the C–O stretching modes of carbonic acid are calculated using the ab initio classical separable potentials approximation. In this approach, ab initio molecular dynamics simulations are used to determine an effective classical potential for each of the normal modes of the system. The frequencies are calculated by solving the time-independent Schrödinger equation for each mode using time-averaged potentials. Hydrogen-bonded carbonic acid dimer, carbonic acid–water complex and isotopologues of these systems were also studied, showing good agreement with experiments. Useful insights are obtained by Fourier transforming the effective potentials, which relates the computed quantum frequencies to the classical dynamics of the system. This approach is illustrated for the systems studied, including for the challenging anharmonic isotope effect. In conclusion, the ab initio CSP approximation yields results in good accord with experiments, and the method provides interpretations in terms of the dynamics of vibrational motions.

碳酸的O–H和C–O拉伸模式的非谐频率是使用从头开始的经典可分离势近似来计算的。在这种方法中，从头开始分子动力学模拟用于确定系统每个正常模式的有效经典势能。通过使用时间平均电势对每种模式求解与时间无关的薛定ding方程来计算频率。还研究了这些系统的氢键合碳酸二聚体，碳酸-水络合物和同位素同聚物，与实验结果吻合良好。有用的见解是通过傅立叶变换有效电势获得的，该电势将计算出的量子频率与系统的经典动力学联系起来。已针对所研究的系统（包括具有挑战性的非谐同位素效应）说明了该方法。总之，从头算起 CSP近似得出的结果与实验非常吻合，并且该方法提供了有关振动运动动力学的解释。