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The interaction of charged dust particles in plasma is often modeled assuming a constant charge on each particle with the particle charge determined by requiring zero net current to the particles when they are far apart. In this paper the variation in particle charge is calculated for two-body encounters of dust particles taking into consideration mutual electrostatic shielding and a finite Debye length λD . Results are reported for particle radii between 0.0105λD and 0.349 λD. Work is also calculated as a function of particle separation, and it is shown that dust particle energies greater than 50 eV are required before the variation in charge becomes significant. It is also demonstrated that for particles with radii greater than λD/10 the plasma can act to increase the force at separations less than 3λD, and it is shown that the Debye–Huckel factor (1+a/ λD) may overestimate particle charge by as much as ten percent for larger particles.