A new approach is presented to improve the performance of semiempirical quantum mechanical (SQM) methods in description noncovalent interactions. To show strategy, PM6 Hamiltonian was selected, although, general, procedure can be applied other Hamiltonians and different methodologies. set small molecules were selected as representative various functional groups, intermolecular potential energy ...

Semiempirical (SE) methods can be derived from either Hartree-Fock or density functional theory by applying systematic approximations, leading to efficient computational schemes that are several orders of magnitude faster than ab initio calculations. Such numerical efficiency, in combination with modern computational facilities and linear scaling algorithms, allows application of SE methods to ...

We present two new methods for molecular dynamics simulations based on general HartreeFock (GHF) theory. The first method involves approximating ab initio STO-3G matrix elements with fitting functions to enable faster computation of the energy and forces for molecular dynamics simulations. The implementation of this method includes a frozen-core approximation. The second method involves develop...

für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namen...

The electronic structure of model platinum-guanine and tin-guanine adducts has been studied both at semiempirical level and by using ab initio methods at the correlation level. The possible binding energies have been evaluated and most probable strustures were determined. In all cases the binding enegies of the gaseous tin chelates are rather large. The stabilizing role of the hydrogen bonds ha...

The maximum absorption wavelengths of 31 azo dyes have been calculated by two comprehensive methods using the semiempirical quantum chemical method, PM3, and the weight decay based artificial neural network (WD-ANN) or the early stopping based artificial neural network (ES-ANN). The average absolute errors of WD-ANN and that of ES-ANN are 10.07 nm and 12.40 nm, respectively. These results are m...

New quaternary alkylammonium conjugates of steroids were obtained by two step reaction of sterols (ergosterol, cholesterol, dihydrocholesterol) with bromoacetic acid bromide, followed by bimolecular nucleophilic substitution with a long chain tertiary alkylamine. The structures of products were confirmed by spectral (1H-NMR, 13C-NMR, and FT-IR) analysis, mass spectrometry and PM5 semiempirical m...