Hellmann Robert
Institut für Thermodynamik, Helmut-Schmidt-Universität/Universität der Bundeswehr Hamburg, Holstenhofweg 85, 22043 Hamburg, Germany.
J Phys Chem B. 2022 Jun 2;126(21):3920-3930. doi: 10.1021/acs.jpcb.2c01830. Epub 2022 May 18.
The second to eighth virial coefficients of methane were determined for temperatures up to 1200 K using an existing ab initio-based and empirically fine-tuned two-body potential combined with a new empirical nonadditive three-body potential. Nuclear quantum effects were accounted for by the semiclassical Feynman-Hibbs approach. The numerical evaluation of the high-dimensional integrals through which the virial coefficients are expressed was performed employing the Mayer-sampling Monte Carlo technique. By fitting suitable mathematical functions to the calculated virial coefficients, an analytical eighth-order virial equation of state (VEOS8) was obtained. Pressures computed as a function of temperature and density ρ using VEOS8 agree highly satisfactorily with (ρ, ) values obtained with the experimentally based reference equation of state for methane of Setzmann and Wagner (SWEOS) at state points at which VEOS8 is sufficiently converged. It is shown that it is essential to account for nonadditive three-body interactions in the calculations in order to achieve good agreement with the SWEOS.
利用现有的基于从头算并经经验微调的两体势与新的经验非加和三体势，确定了温度高达1200 K时甲烷的第二至第八维里系数。通过半经典的费曼-希布斯方法考虑了核量子效应。采用迈耶抽样蒙特卡罗技术对表示维里系数的高维积分进行数值计算。通过将合适的数学函数拟合到计算得到的维里系数上，得到了一个解析的八阶维里状态方程（VEOS8）。在VEOS8充分收敛的状态点，使用VEOS8计算得到的作为温度和密度ρ函数的压力与使用基于实验的塞茨曼和瓦格纳甲烷参考状态方程（SWEOS）得到的（ρ, ）值高度吻合。结果表明，为了与SWEOS取得良好的一致性，在计算中考虑非加和三体相互作用至关重要。
