## DERIVATION OF QUADRATIC VIRIAL EQUATION OF STATE BY MODIFIED CANONICAL ENSEMBLE METHOD

**HU Jia wen, TANG Ming lin, YIN Hui an (Chengdu University of Technology, China)**

In the canonical ensemble distribution function Q , the total interactive energies between any selected molecule and all the other N-1 ones are converted to N-1 times of the interactive energies of an arbitrary pair of molecules among them multiplied by a rectification coefficient, and the product is regarded as a function only depending on the coordinates of the selected pair of molecules. Then, distribution function Q can be transformed into a product of integrals of N /2 pairs of molecules. The cluster integral expansion method is used to derive the integral constant, whose simplified form is substituted into Q . The former two terms in the logarithm expansion of Q are substituted into the definition expression of pressure in the canonical ensemble theory. In this way, quadratic virial equation of state can be derived reasonably, thus the mathematical difficulty in the classical canonical ensemble method is eliminated.

【CateGory Index】：
O414.2

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