CompuServe Thread

Thanks. Your reply seems to verify much of what I suspected. A few semi-random comments in reply follow. When I stated that molecular mechanics turned off the periodic boundary conditions, I really meant that molecular DYNAMICS seem to turn off the periodic boundary conditions. At least that's what I recall from attempting it and remember reading somewhere in one of your three (well written) manuals (which I alas have left in my office). Your state <2. The box is equilibrated to a 300K box of water, so the arrangement of molecules is pretty good as a starting point.> This implies that I could carry out a molecular mechanics calculation in a periodic box until convergence was reached. It should then be possible to allow the geometries (of solute and solvent) to relax using a semi-empirical calculation such as AM-1. I suspect that few molecules would diffuse away under such conditions. You further state <We don't have periodic boundary conditions for semi-empirical methods, but those calculations on a box of any size would take forever and a day anyway> This is a matter of personal opinion (in my personal opinion). Computers are typically turned off at the end of each work day. There is frequently significant availble unused time on most pc's which surround me. The 486 DX2 which I use is however always running even when business interests turn my attention (sometimes for prolonged periods) to matters far removed from chemistry theory. I read somewhere that novices in the field of molecular modelling often make the mistake of calculating too much too quickly. I guess what I'm trying to say is please don't assume that what is slow for some is too slow for everybody. After all, most of us have to go on vacation some time. One of your competitors told me that organic chemists had no need for carring out ab initio calculations on a pc if the calulations would take two weeks to a month (it seemed to escape him that I [>> Continued in next msg]