<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On May 15, 2009, at 10:40 AM, Tom Goddard wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi Armida,<br><br> Elaine is right. The atoms are weighted by their mass, carbon counts <br>12 times more than a hydrogen. Isotopic abundances are not considered <br>-- I think Chimera's atom.element.mass is just the number of protons <br>plus neutrons in the post prevalent isotope.</div></blockquote><br></div><div>The mass is the number from the periodic table of the elements -- which is an average across isotopes.</div><div><br></div><div>--Eric</div><div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="5" style="font: normal normal normal 16px/normal Helvetica; "><br class="Apple-interchange-newline"> Eric Pettersen</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="5" style="font: normal normal normal 16px/normal Helvetica; "> UCSF Computer Graphics Lab</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="5" style="font: normal normal normal 16px/normal Helvetica; "> <a href="http://www.cgl.ucsf.edu">http://www.cgl.ucsf.edu</a></font></div></div></div><br><div></div></body></html>