Electrostatic potential (ESP) derived partial charge provides a useful tool for describing intermolecular electrostatic (ES) interactions. One can also devise a corresponding charge "operator" that generates partial charge upon taking the expectation value over molecular wavefunctions. While the ESP charge operator has been utilized in various QM/MM(-type) calculations, it has the drawback that short-range ES interactions are overestimated due to the neglect of charge penetration effects. Here, we develop a screened version of the ESP charge operator that includes penetration effects at short range and thereby improve its accuracy. Numerical tests are performed for typical ions in aqueous solution. (C) 2012 Elsevier B.V. All rights reserved.