Abstract
The purpose of this research is to investigate the accuracy of the intermolecular potential energies, which were calculated with different quantum chemistry methods and basis sets. The quantum chemistry methods that were used in this research are MP2 and CCSD(T), and the basis sets are aug-cc-pVXZ (X= D, T, Q). The most important part of the calculating methods is to add bond function in the calculations, and therefore by comparing the results between calculations with and without bond function, this research proved that with the use of bond function in the calculation, we can improve the calculating results. In other words, even if we used lower theory levels or decreased the number of basis sets in the calculations, we can still acquire accurate results, and therefore save a large amount of time. By calculating the intermolecular potentials between argon and CF4, we may confirm the advantages of the use of bond function we have mentioned above. Hence, the bond function is also added when calculating the intermolecular potentials between CF4 and CF4. Before the calculation started, the orientations of the molecules need to be built. Then, we calculated the intermolecular potential energies with different distances between molecules. The software we use to do the calculation is GAUSSIAN03. The results, which were based on different quantum chemistry methods and basis sets, were then compared and discussed. The calculated results were fitted with Buckingham Potential and the parameters of the Buckingham Potential were found by a program, which is built by C++ and based on an algorithm that is to transform a non-linear function into a linear one. The gene algorithm was used to improve the parameters we acquired by the previous program.