A Simple Method for Incorporating Madelung Field Effects into ab Initio Embedded Cluster Calculations of Crystals and Macromolecules

A new methodology is proposed for accurate and effective incorporation of the matrix elements of the Madelung potential into ab initio embedded cluster calculations of macromolecules, polar crystals, and their surfaces. The electrostatic potential from the infinite crystal lattice is modeled by a finite number (usually several hundred) of point charges located on a surface enclosing the cluster. A special boundary condition and the boundary element method are used to determine positions and magnitudes of these point charges. The advantages and accuracy of this approach are demonstrated on examples of water adsorption on the NaCl(001) surface and the electrostatic field in a zeolite pore.