A distance-dependent dielectric coefficient (RDIE: ) has been used to approximate solvent screening without including explicit water molecules. Physically, it's a pretty ugly way to cheat. But if you don't want to include water, it may be the best your simulation package has to offer; it is almost certainly better than using unscreened partial charges in the absence of water. For realistic dynamics, we recommend constant-dielectric (CDIE) simulations with explicit solvation and . The presence of water retards conformational searching, however.
The SHIFt option does a good job of monotonically damping a force (RDIE electrostatics) to zero. Use of CTOFnb = 10 Åshould suffice. Although simulations have definitely evolved toward explicit solvation with true Coulombic forces (CDIE), RDIE SHIFt is arguably the best choice (in CHARMM) when the inclusion of explicit water remains prohibitively expensive.