Date of Award
Chemistry and Biochemistry
This work characterizes five stationary points of the formaldehyde dimer, (CH2O)2, two of which are minima, seven newly-identified stationary points of the formaldehyde/thioformaldehyde (mixed) dimer, CH2O/CH2S, four of which are minima, and five newly-identified stationary points of the thioformaldehyde dimer, (CH2S)2 , three of which are minima. Full geometry optimizations and corresponding harmonic vibrational frequencies were performed on CH2O and CH2S as well as each of the dimer configurations (Figures 3-5). The computations were carried out with second order MÃ¸ller-Plesset perturbation theory (MP2), with the heavy-auc-cc-pVTZ (haTZ) basis set. Additionally, thirteen density functional theory methods were employed: B3LYP, B3LYP-D3, B3LYP-D3(BJ), TPSS, TPSS-D3, TPSS-D3(BJ), APF, APF-D, M06-2X, M06-2X-D3, N12SX, MN12SX, and VSXC, in conjunction with the 6-311+G(2df,2pd) basis set. Six of these functionals are dispersion corrected with either the original D3 damping function (DFT-D3) or the Becke-Johnson damping function [DFT-D3(BJ)]. Binding energies were computed via the supermolecular approach. Single-point energies were also computed for all optimized structures using explicitly correlated MP2-F12 and CCSD(T)-F12 methods with the haTZ basis set. The (CH2O)2 and CH2O/CH2S global minimum are the same at the MP2, MP2-F12, and CCSD(T) levels of theory. However, MP2 methods overbind (CH2S)2 by as much as 1.1 kcal mol-1, effectively altering the energetic ordering of the (CH2S)2 minima relative to the CCSD(T)-F12 energies.
Holy, Christina M., "Anchoring the Potential Energy Surfaces of Homogenous and Heterogenous Dimers of Formaldehyde and Thiofomaldehyde" (2014). Honors Theses. 193.