Ab-initio calculation method for charged slab systems using   field-induced gaussian sheet
  A new repeated-slab calculation method is developed to simulate the electronic structures of charged surfaces by arranging density-variable charged sheets in vacuum regions to realize a constant potential on the charged sheets and maintain the charge neutrality condition. The charged sheets are fabricated so as to screen an electric field from charged slabs; consequently, they act like a counter electrode composed of flat perfect conductors, modeling a tip of a scanning tunneling microscope or a reference electrode in an electrochemical cell. This method has the advantages of ease of implementation into existing repeated-slab programs and low computational costs. 
Seiji Kajita, Takashi Nakayama, Maki Kawai