Exploring NH3–NH3 interactions: A comparative study of force field and CCSD(T)/QZVPP calculations for thermodynamic analysis and second virial coefficient in gas-phase chemistry and atmospheric science

Abstract

In this study, we investigate the quadrupole moment of ammonia (NH₃) using the coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)] and the quadruple-zeta valence plus polarization (QZVPP) basis set. The calculated values for the quadrupole moment, polarizability, and entropy of NH₃ (−2.44 a.u, 2.113 Å³, 192.69 JK⁻¹mol⁻¹) are in excellent agreement with the corresponding experimental values (−2.45 a.u, 2.109 Å³, 192.77 JK⁻¹mol⁻¹) respectively. The vibrational mode of frequencies of ammonia is close to calculated values. Additionally, we explore the application of ILJP parameters (ILJPP) to determine the SVC B of NH₃. By employing the ILJP limitations, we obtain calculated values of B that exhibit a remarkable agreement with the experimental values. This result highlights the accurateness and reliability of the ILJP in describing the intermolecular interactions of NH₃ dimer. Our findings demonstrate the capability of the CCSD(T)/QZVPP method to accurately determine the quadrupole moment of NH₃, validating its agreement with experimental values. Furthermore, the successful implementation of ILJPP to calculate the SVC emphasizes the effectiveness of this approach in capturing the thermodynamic properties of NH₃. This research contributes to a deeper understanding of NH₃'s molecular properties and facilitates its application in various scientific and technological domains. In gas-phase chemistry, knowledge of ammonia-ammonia interactions is essential for predicting reaction rates, exploring molecular dynamics, and understanding gas-phase equilibria involving ammonia. Furthermore, in atmospheric science, studying NH₃–NH₃ interactions can contribute to our understanding of ammonia's role in air pollution, aerosol formation, and acid deposition.