Improvements in the generalized hybrid orbital method

Abstract

In a previous paper, we described the adaptation of the generalized hybrid orbital (GHO) method for the use in fragment based quantum chemical approaches for large molecules like the field-adapted adjustable density matrix assembler (FA-ADMA). It soon became evident that the limitations of the available implementation strongly restrict its use. Therefore, in the article presented here, we describe new developments to circumvent these limitations. These include new construction algorithms of the GHO hybrid orbitals for sp 3- as well as sp2-hybridized carbon and nitrogen, different distributions of electrons in the auxiliary orbitals, and the separation from the CHARMM program, which was needed to provide partial charges and bonding information. The results demonstrate an excellent improvement in accuracy of the obtained electron densities compared to capping hydrogen atoms. Additionally, the calculation of gradients opens the possibility to use FA-ADMA for geometry optimization of large molecules. © 2009 Wiley Periodicals, Inc.