Leforestier Claude
Institut Charles Gerhardt, CNRS 5253, CC 15.01, Université Montpellier II-CNRS, 34095 Montpellier Cedex 05, France.
J Chem Phys. 2014 Feb 21;140(7):074106. doi: 10.1063/1.4865339.
We present a full quantum evaluation of the water second virial coefficient B(T) based on the Takahashi-Imada second order approximation. As the associated trace T r[e(-βH(AB)) - e(-βH(0)(AB))] is performed in the coordinate representation, it does also include contribution from the whole continuum, i.e., resonances and collision pairs of monomers. This approach is compared to a Path Integral Monte Carlo evaluation of this coefficient by Schenter [J. Chem. Phys. 117, 6573 (2002)] for the TIP4P potential and shown to give extremely close results in the low temperature range (250-450 K) reported. Using a recent ab initio flexible potential for the water dimer, this new formulation leads to very good agreement with experimental values over the whole range of temperatures available. The virial coefficient is then used in the well known relation Kp(T) = -(B(T) - bM)/RT where the excluded volume bM is assimilated to the second virial coefficient of pure water monomer vapor and approximated from the inner repulsive part of the interaction potential. This definition, which renders bM temperature dependent, allows us to retrieve the 38 cm(3) mol(-1) value commonly used, at room temperature. The resulting values for Kp(T) are in agreement with available experimental data obtained from infrared absorption spectra of water vapor.
我们基于高桥 - 今田二阶近似对水的第二维里系数(B(T))进行了全量子评估。由于相关的迹(Tr[e^{(-βH(AB))} - e^{(-βH(0)(AB))}])是在坐标表象中进行的，它也包含了整个连续统的贡献，即单体的共振态和碰撞对。将这种方法与申特（Schenter）[《化学物理杂志》117, 6573 (2002)]针对TIP4P势对该系数进行的路径积分蒙特卡罗评估进行了比较，结果表明在报道的低温范围（250 - 450 K）内两者给出的结果极为接近。使用最近针对水二聚体的从头算柔性势，这种新公式在整个可用温度范围内都与实验值取得了很好的一致性。然后将维里系数用于著名的关系式(Kp(T) = -(B(T) - bM)/RT)，其中排斥体积(bM)被视为纯水单体蒸汽的第二维里系数，并从相互作用势的内部排斥部分进行近似。这个使(bM)与温度相关的定义，让我们能够得到在室温下通常使用的(38 cm^3 mol^{-1})值。由此得到的(Kp(T))值与从水蒸气红外吸收光谱获得的现有实验数据一致。
