From chemistry-request@server.ccl.net Sat Feb 22 02:49:02 2003 Received: from ns0.scripps.edu ([192.42.82.58]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id h1M7n2a22901 for ; Sat, 22 Feb 2003 02:49:02 -0500 Received: from antigen.scripps.edu (antigen.scripps.edu [137.131.200.100]) by ns0.scripps.edu (8.11.6/TSRI-4.1rx) with SMTP id h1M7n2819028 for ; Fri, 21 Feb 2003 23:49:02 -0800 (PST) Received: from relay1.scripps.edu(137.131.200.29) by antigen.scripps.edu via csmap id 4064; Fri, 21 Feb 2003 23:41:28 -0800 (PST) Received: from gamow.scripps.edu (gamow.scripps.edu [137.131.252.67]) by relay1.scripps.edu (8.11.6/TSRI-4.2rAV) with ESMTP id h1M7mpZ19579; Fri, 21 Feb 2003 23:48:51 -0800 (PST) Received: from quine.scripps.edu (gamow [137.131.252.67]) by gamow.scripps.edu (8.9.2/TSRI-3.0.1) with SMTP id XAA90282; Fri, 21 Feb 2003 23:48:50 -0800 (PST) Received: by quine.scripps.edu (sSMTP sendmail emulation); Fri, 21 Feb 2003 23:48:43 -0800 Date: Fri, 21 Feb 2003 23:48:43 -0800 From: "David A. Case" To: M Brunsteiner Cc: chemistry@ccl.net Subject: Re: CCL:system size and pressure correlations in MD Message-ID: <20030222074843.GA2404@scripps.edu> References: <3E54C35F.1F4D8F22@ucl.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3E54C35F.1F4D8F22@ucl.ac.uk> User-Agent: Mutt/1.4i On Thu, Feb 20, 2003, M Brunsteiner wrote: > > I am looking for information on pressure > correlations in liquds. If I did a molecular > dynamics simulation, how would the size of the > pressure fluctuations depend on the system size > (the box-size in an MD simulation) The simplest place I know to look for information on this is section 114 of "Statistical Physics", by Landau and Lifshitz. With some (seemingly reasonable) approximations, the mean square fluctuations in pressure are given by kT/(V*beta), where beta is the compressibility. Hence, roughly, the pressure fluctuations should scale as the inverse square root of the volume. Many moons ago, I ran some water simulations on various box sizes, that seemed to bear this out, but you should probably check things yourself. ..hope this helps...dac -- ================================================================== David A. Case | e-mail: case@scripps.edu Dept. of Molecular Biology, TPC15 | fax: +1-858-784-8896 The Scripps Research Institute | phone: +1-858-784-9768 10550 N. Torrey Pines Rd. | home page: La Jolla CA 92037 USA | http://www.scripps.edu/case ==================================================================