High-level ab initio studies of amino acid conformations, rotamerizations, and tunneling dynamics
MetadataShow full item record
The effects of intramolecular forces on molecular geometries, energies, and dynamics are presented for various molecular prototypes. High-accuracy relative energies of glycine and serine conformers and barriers for their conformational interconversions are computed via focal point analyses. Quantum tunneling is investigated within a reaction-path Hamiltonian model with transmission probabilities given by standard methods. The half-lives of the multiple interconversions among the eight glycine conformers show that conformer IVn has escaped detection due to fast rotational tunneling to the global minimum Ip. The complex conformational space of serine is investigated, and the relationship between intramolecular hydrogen bonds and conformational structures is examined. A total of 85 conformers of serine are located through an exhaustive conformational search with delicately balanced levels of theories. A general categorizing scheme based on the interactions between the amine and carboxylic acid groups is proposed. Finally, we show how the Coulomb operator within two-electron integrals can be split into long- and short-range pieces to unravel the correlation energy dependence on the electron-electron interaction distance within rigorous wave functions. This analysis seeks to place intra- and intermolecular dispersion on an equal footing and challenges common understandings of these phenomena.