New version of UBDB databank andLSDBprogram, verification and applications
Katarzyna Natalia Jarzembska, P. M. Dominiak · Acta Crystallographica Section A Foundations of Crystallography · 2011
Popular force fields usually employ point charges.Supplementing atomic charges with higher electrostatic multipole moments leads to more accurate charge distribution models.New generation force fields based on multipole models require high level of transferability of atomic multipoles.The aim of this work was to analyze the level of transferability achievable with the use of different methods of molecular density partitioning.Molecular densities (MDs) were calculated for selected natural amino acids as well as di-and tripeptides in geometries as observed in X-ray diffraction experiment.The MDs were obtained through Fourier space fitting of pseudoatom model to the electron densities resulting from ab initio DFT calculations at B3LYP/6-31G** level.Such procedure was selected in order to be compatible with the idea of building a pseudoatom database [1-3] pursued in the charge density crystallography.Atomic multipole moments expressed in local coordinate system were calculated on the basis of three density partitions: directly from pseudoatoms, from atomic densities computed via stockholder partitioning and from atomic basins derived via topological analysis.Standard deviations from averaging over multipole moment components of atoms that are considered equal in their chemical environments (atoms representing the same atom type) were chosen as a measure of transferability.The advantage of stockholder partition as yielding the best transferability within considered atom types was observed.The results were compared to the calculations of atomic multipoles directly from molecular wave functions (in atomic basins partition).