Ab initio simulation of the effect of the potential of water on the electronic structure of arginine.

As a part of the task of constructing the equivalent potential of water in order to obtain a reliable electronic structure for a protein, the equivalent potential of water for an arginine molecule was constructed by performing first-principles, all-electron, ab initio calculations. The process consisted of three steps. First, the electronic structure of arginine was calculated using a free cluster calculation. Then, the minimum-energy geometric structure of the system Arg(+)+9H(2)O was found using free cluster calculations. Then, based on the optimized geometric structure of the Arg(+)+9H(2)O system, the electronic structure of Arg(+) in the potential of water was calculated using the SCCE method. Finally, by performing SCCE calculations, the effect of water on the electronic structure of Arg(+) was simulated with dipoles. The results show that the effect of water on the electronic structure of Arg(+) is to broaden the energy gap tenfold, and to increase the eight eigenvalues below the HOMO by about 0.0546 Ry on average. The water potential can be accurately simulated using dipoles.