Energy conservation of molecular dynamics in the presence of electrostatic forces

 Dear CCLers,
 I have a general question about totoal energy conservation of classical
 molecular dynamics (MD) in the presence of electrostatic forces.
 Total energy is perfectly conserved when we do a typical MD with
 only the wan der Waals (Lennard-Jones) potentials, using a time
 step of one femtosecond (e.g. for the Argon gas as a classical example).
 Problems, however, arise when molecules are charged. Because
 electrostatic forces are much more long-ranged (1/r dependence) and
 typically stronger, the magnitude of electrostatic forces on atoms can
 be several hundred (or even thousand) times greater than that of van
 der Waals forces. As a result, the time step has to be accordingly
 reduced for two or three orders of magnitude, in order for the total
 energy to conserve. This means a time step of 0.001-0.01 femtosecond
 has to be applied.
 (EXPLAIN: Most standard algorithms, such as the Verlet method, the Gear
 predictor-corrector method and the Runge-Cutta method, depend on using
the term a*dt^2 to compute the solution stepwisely, where a is the acceleration, dt is the time step. If this term is too large, the numerical error will rapidly 
 propogate, and the solution will diverge. Compared with pure Lennard-Jones
simulations, adding the electrostatic forces increase accelerations. Therefore, 
 dt must be decreased in order to keep a*dt^2 down.)
 I can see only two ways to solve this problem, both of which turn out to be
 impractical, as you will see later.
 One is to accept the reality, use a smaller time step. But, reducing the time
 step to 0.001 femtosecond will slow down the simulation 1000 times (in
 comparison to pure Lennard-Jones simulations). You will probably never see
 any emerging behavior of the model because losing your temper.
 The other way around is to use smaller charges, as most molecular mechanics
 force fields do. For example, instead of using 1 for a free radical's charge,
one can use 0.01 (and self-explain that this is an effective-field approximation). 
 While this would maintain energy conservation, you might not see the
 emerging behaviors due to charges either --- because the electrostatic forces
 are so weaker than they ought to be, they might not be able to produce
 results that only strong interactions can exhibit, such as self-organization.
 Energy conservation is generally not an concern for most classic molecular
 dynamics simulations that assume a heat bath (for controlling the temperature
to a desired value, thus remove the numerical errors resulted from large a*dt^2). 
 However, getting the energetics right is of paramount importance to modeling
 exoergicity/endoergicity of chemical reactions. Unfortunately, I am not aware
 of anyone mentioning this before. All the molecular simulation books I have
 (Allen and Tildesley, Leach, Rapaport and so on) do not even mention it at all.
My prior experience with CHARMm v27, if I was doing it right, is that it doesn't seem to do energy conservation, even though the NVE protocol is literally specified. 
 I would greatly appreciate any advice and opinion.
 Thank you,
 Charles Xie
 International Center
 The Concord Consortium
 www.concord.org