Practical limitations observed using the AM1, MNDO and MINDO/3 semi-empirical methods for charge calculation and structure optimization in 1,2,4-triazine ring-containing compounds

摘要

An investigation employing the semi-empirical AM 1, MNDO and MINDO/3 methods in the program package ampac to calculate both electronic charge distribution and structure optimization on compounds containing a 1,2,4-triazine ring moiety has been undertaken. Significant errors are found in the results obtained, when compared with known crystal-lographic data, in bond lengths, bond angles and dihedral angles of the optimized structures. Also from crystallographic diilii the charges calculated for the experimentally determined and optimized structures are shown to be inaccurate. These results severely question the use of these semi-empirical approaches in heleroaromatie compounds containing nitrogen nitrogen ring bonds.