Lately, there has been great interest in performing free-energy perturbation (FEP) at the combined quantum mechanics and molecular mechanics (QM/MM) level, e.g. for enzyme reactions. Such calculations require extensive sampling of phase space, which typically is prohibitive with density-functional theory or ab initio methods. Therefore, such calculations have mostly been performed with semiempi...

A comparative study of ab initio 6-31G(*) and semiempirical modified neglect of differential overlap (MNDO) bond orders and MNDO diatomic energy contributions for the description of bond strengths in neutral and protonated glycine, diglycine, triglycine, and dialanine is presented. Good correlations were found between 6-31G(*) and MNDO bond orders and between MNDO bond orders and diatomic energ...

the conformation of alinidine a new and specific bradycardic agent was studied using mndo method. it has been found that the rotation of both phenyl and imidazoline ring of this compound is restricted. of two possible isomers of irnidazoline ring, the one with nh in the cis position to allyl side chain is slightly more stable. on the other hand, the allyl group can rotate freely and at least si...

Atomic surface tensions are parameterized for use with solvation models in which the electrostatic part of the calculation is based on the conductor-like screening model (COSMO) and the semiempirical molecular orbital methods AM1, PM3, and MNDO/d. The convergence of the calculated polarization free energies with respect to the numerical parameters of the electrostatic calculations is first exam...

The conformation of alinidine a new and specific bradycardic agent was studied using MNDO method. It has been found that the rotation of both phenyl and imidazoline ring of this compound is restricted. Of two possible isomers of irnidazoline ring, the one with NH in the cis position to allyl side chain is slightly more stable. On the other hand, the allyl group can rotate freely and at leas...

the ability of the present semiempirical quantum mechanics methods are surveyed for reproducing the transannular interaction in the bifunctional n-phenyl-5-azocanones. the am1 method is the best with the order of reliability being am1, pm3, mndo and mindo/3. am1 calculations were then carried out for quantification of transannular interaction. the n(o) ionization potential has been used for thi...

The ability of the present semiempirical quantum mechanics methods are surveyed for reproducing the transannular interaction in the bifunctional N-phenyl-5-azocanones. The AM1 method is the best with the order of reliability being Am1, PM3, MNDO and MINDO/3. AM1 calculations were then carried out for quantification of transannular interaction. The n(o) ionization potential has be...

Gas phase and aqueous phase quantum chemical calculations for the inhibition efficiency of some substituted Benzothiazole (BTH) and its 2-methyl (MeBTH), 2-amino (ABTH), 2-mercapto (MBTH) and 2-phenyl (PhBTH) as corrosion inhibitors for brass in HClO4 were investigated by means of the AM1, PM6, MNDO and RM1 semi-empirical SCF molecular orbital methods. The calculated quantum chemical parameters...