Lab 4 Gaussian Equation

Christine Woelfel-Monsivais
10/13/14
Chem 4448.13
Lab 4: Gaussian Calculations
Introduction
The purpose of the lab was to gain a better understanding of the Gaussian calculations and see how the obtained calculations can be used to explore the chemistry of the atoms. In this lab several molecules were created and given specific bond lengths before running a Gaussian test for optimization and frequency. Through this test the vibrational frequency, force constant, reduced mass and point group were obtained for each of the molecules created. In addition the energy in Hartee for each molecule was also obtained. The molecules used were Iodine (I2), Carbon Monoxide (CO), Cyanide ion (CN-), Acetonitrile (CH3CN) and Benzene (C6H6). The energy equations used previously allows one to solve the Schrodinger equation for molecular energies. The Hamiltonian operator in the energy equation, containing the electron correlation is more complicated and cannot be solved. The electron correlation is the interaction of electrons with other electrons. There are several model chemistry examples used to approximate including, molecular mechanics, ab-inito, configuration interaction, semi-empirical,
The table shows several trends such as, the bond length decreasing as the molecular weight of the molecules increases. This shows that the bond length is inversely proportional to the molecular weight. Another trend seen in Table 1 is that the bond length decreases as the vibrational frequencies increase. This shows that as the molecule gets larger so does the vibrational frequency. Also the reduced mass gets smaller as the molecules get larger, while the force constant get larger as the molecules get larger. The point groups for acetonitrile and benzene are C3v and D3h respectively, which are the expected point groups for the two