Comparison of quantum chemistry calculation methods of nucleic acid base-quartets

Nine base-quartets were calculated by six semi-empirical methods and ab ini tio Hartree-Fork method using STO-3G basis set. The results showed that PM3 method can be use to calculate base quartets, the results of PM3 calculati ons are close to the ab initio calculations. The achieved stabilization ord er of the base-quartets pointed out that a base quartet would be formed by way of base pairs, and a new base quartet G.C.G.C VII might exist in variou s DNA except three base-quartets found experimentally, G-quartet, U-quartet , and G.C.G.C quartet.