From owner-chemistry@ccl.net Sat Apr 20 06:47:49 1996 Received: from bedrock.ccl.net for owner-chemistry@ccl.net by www.ccl.net (8.7.1/950822.1) id GAA18589; Sat, 20 Apr 1996 06:20:04 -0400 (EDT) Received: from ursa.cus.cam.ac.uk for rlm1003@cus.cam.ac.uk by bedrock.ccl.net (8.7.1/950822.1) id GAA19605; Sat, 20 Apr 1996 06:20:02 -0400 (EDT) Received: from apus.cus.cam.ac.uk [131.111.8.2] (ident = root) by ursa.cus.cam.ac.uk with smtp (Smail-3.1.29.0 #77) id m0uAZlo-00011CC; Sat, 20 Apr 96 11:20 BST Received: by apus.cus.cam.ac.uk (Smail-3.1.29.0 #36) id m0uAZlm-00033yC; Sat, 20 Apr 96 11:19 BST Message-Id: Date: Sat, 20 Apr 96 11:19 BST From: rlm1003@cus.cam.ac.uk (Ricardo) To: CHEMISTRY@ccl.net Subject: CCL: Spherical truncation in simulations Dear netters, I'm simulating water using the Ewald sum, on one hand, and using a straight spherical truncation of the electrostatic interactions, on the other. I'm doing NPT Monte Carlo runs near room temperature. My problem is that, while I get the right density using the Ewald sum, when I use spherical truncation the density is smaller by about 10%. Is this sort of effect to be expected when long-range forces are treated by simply truncating them at a given cutoff? Any comments and/or references would be much appreciated. R. L. Mancera Department of Chemistry University of Cambridge Lensfield Road Cambridge CB2 1EW, UK Tel: +44 1223 336353 Fax: +44 1223 336362 E-mail: rlm1003@cus.cam.ac.uk