A Method for the Numerical Evaluation of the Second Virial Coefficient for Polyatomic Molecules.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Thermodynamics

Background:

• The second virial coefficient is crucial for understanding gas behavior and intermolecular forces.
• Accurate calculation of the second virial coefficient for polyatomic molecules is complex due to anisotropic interactions.

Purpose of the Study:

• To develop a numerical integration procedure for calculating the second virial coefficient of simple polyatomic molecules.
• To assess the accuracy of the proposed method for quadrupolar and dipolar molecules.

Main Methods:

• The intermolecular pair potential is modeled as a sum of spherically symmetric and angular-dependent terms.
• The method involves evaluating different numerical values for the angular-dependent contribution.
• Numerical integration is applied to compute the second virial coefficient.

Main Results:

• The proposed method provides accurate second virial coefficients for quadrupolar molecules (within 1 part in 2500) and polar molecules (within 1 part in 300).
• Comparison with the Pople expansion shows the proposed method's reliability.
• The study highlights the need for careful application of the Pople expansion to ensure convergence.

Conclusions:

• The developed numerical integration procedure is a reliable and accurate tool for calculating the second virial coefficient of simple polyatomic molecules.
• The method offers a valuable alternative to existing techniques, particularly when dealing with anisotropic intermolecular potentials.
• Ensuring convergence in related computational methods like the Pople expansion is critical for accurate results.