Semiempirical QM and Ewald Sum
| The Ewald lattice-sum method has been incorporated into
semiempirical QM/MM calculations for periodic systems. The method is based on a
Ewald sum QM/MM Hamiltonian, with semiempirical electronic integral evaluation scheme.
It takes advantage of the multipole expansion algorithm of the Dewar-Thiel model
for two-electron integral calculations. Thus, the key feature of the Ewald-QM/MM
method is to determine the electrostatic potential of the periodic system at the charge
expansion sites. A number of layers of approximations may be adopted to evaluate the Klopman-Ohno damping factor within the Ewald-sum algorithm and to reduce the computation costs. These methods have been incorporated into the MCQUB program, and a detailed description can be found in J. Chem. Phys. 107, 1212 (1997). |