Reaction energetics of tetrahedrane and other hydrocarbons: Ab initio and density functional treatments

Abstract

Reaction energetics of the highly strained tetrahedrane molecule, as well as some smaller hydrocarbons, were computed at the ab initio MP4, QCISD (T), G1, and G2 levels and also by several density functional (DF) approaches: VWN(LDA), PW86, BLYP, and B3LYP. A variety of basis sets were used in the DF calculations. For atomization processes, nonlocal DF procedures are superior to MP4 and QCI. For the other reactions, B3LYP is the most reliable DF approach and is overall competitive with MP4 and QCISD (T), although the MP4/6-3llG(2d', p ) results are generally the closest to the experimental and/or the G2 values. There is no consistent correlation between the accuracy of the DF results and the size of the basis set.

Parameters for molecular dynamics simulations of iron‐sulfur proteins

“…The force constants were obtained through the application of Seminario's method . In this method, the force constants are obtained from the Hessian based on Cartesian coordinates, obtained from frequency calculations.…”

“…This is an area of ongoing research, in which many research groups are working to get the parameters of potential energy functions for general application to biological molecules. In our study, we have adopted Seminario's method to derive force constants for bond stretching and angle bending of iron‐sulfur metalloproteins, to be compatible with the AMBER force field. In this method, the force constants are obtained directly from the Hessian matrix, more exactly from the 3 × 3 submatrices of the pairs of atoms to parameterize.…”

Comparison of Various Quantum Chemistry Methods for the Computation of Equilibrium Constants

“…Indeed, most theoretical papers concerning thermodynamics predictions from quantum results present only ∆H results, more often than not ∆H at 0 K (i.e., ∆E only with ZPE correction). [16][17][18][19][20][21][22][23] Nevertheless, the equilibrium constant is a practical indicator to test theoretical methods because it is very sensitive both to the energy quality and to geometrical parameters and also because the electronic structure of each compound that takes part in the equilibrium is extremely different from the others. Moreover, the ability of theoretical methods to give good equilibrium constants is important to study next the nonideality effect of gases at high pressure.…”