<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><BR><DIV><DIV>On Dec 22, 2005, at 10:37 AM, 主月 ：） wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"> <DIV> <DIV><FONT face="幼圆"><FONT color="#008000">Hi e<FONT face="幼圆">veryone:</FONT></FONT></FONT></DIV> <DIV><FONT face="幼圆" color="#008000">In the manual it said "If you don’t know which one to select we recommend Gromos96 for united-atom setups and<BR>OPLS-AA/L for all-atom parameters." also "GROMOS-96 is not, however, recommended for use with long alkanes and lipids."</FONT></DIV> <DIV><FONT face="幼圆" color="#ff0000"><FONT color="#008000">Now i want to simulate very simple polymer polyethylene C300H602 and i will use CH2 as united atom.</FONT> Which force field is fit current simulation?</FONT></DIV></DIV></BLOCKQUOTE></DIV><DIV><BR class="khtml-block-placeholder"></DIV>Neither. Polymer scientists have developed their own force fields using features like anisotropic united atoms. I'm certainly not an expert in that field, but you can download the Gromacs benchmarks and have a look at the d.polych2 system for an example.<DIV><BR class="khtml-block-placeholder"></DIV><DIV>Cheers,</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Erik<DIV><BR><DIV> <SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><DIV>-----------------------------------------------------------</DIV><DIV>Erik Lindahl <<A href="mailto:lindahl@sbc.su.se">lindahl@sbc.su.se</A>> Backup address: <<A href="mailto:erik.lindahl@gmail.com">erik.lindahl@gmail.com</A>></DIV><DIV>Assistant Professor, Computational Structural Biology</DIV><DIV>Stockholm Bioinformatics Center, Stockholm University, SE 106 91 Stockholm</DIV><DIV>Phone: +46 8 5537 8564 Fax: +46 8 5537 8214</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><BR class="Apple-interchange-newline"></SPAN></SPAN> </DIV><BR></DIV></DIV></BODY></HTML>