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<TITLE>Units of Charge Density - Again</TITLE>
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<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="Calibri">There have been a number of posts to pw_forum regarding the units employed for charge density throughout PWscf package</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> and XcrySDen. This is an importan</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">t issue, and I still find the situation</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> and answers</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">provided in</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> the forum archives</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> ambiguous.</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> Before slogging through</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">relevant source codes,</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">and testing</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">by</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">writing</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> time-consuming</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> homemade examples,</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">I</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">’</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">m hoping someone in the community has preceded me.</FONT></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="Calibri">In a perfect</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">SI</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">world, these units would be</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">coulombs per cubic meter. In a practical</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">, or rather intuitive,</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">world, they would be in units</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">of</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">total fractional number of electrons per unit cell volume (in cubic</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">angstroms or nanometers or bohrs (ugh)).</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> So</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">…</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">what is it? And does it depend on the division of states between core and valence taken when constructing a given ps</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">eudopotential? </FONT></SPAN><SPAN LANG="en-us"> </SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="Calibri">Finally, I</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">’</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">ve been unable</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> (by visual in</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">spection)</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> to determine from the documentation for Xc</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">r</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">y</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">SDen (a marvelous tool</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">…</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">marvelous</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">)</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">, exactly how the</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">“</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">rho grid input</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">”</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> is scaled, especially regarding the</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">computation of the 3D min-max grid values,</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">the</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">“</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">isovalue</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">”…</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">and</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">…</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">particularly</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> the mysterious</FONT></SPAN><SPAN LANG="en-us"> <FONT FACE="Calibri">“</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">delta n(r)</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri">”</FONT></SPAN><SPAN LANG="en-us"><FONT FACE="Calibri"> displayed in the temperature inset box.</FONT></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><B><I></I></B></SPAN><SPAN LANG="en-us"><B><I></I></B></SPAN><B><I><SPAN LANG="en-us"></SPAN></I></B><B><I><SPAN LANG="en-us"><FONT SIZE=4 FACE="Comic Sans MS">Paul M. Grant, PhD</FONT></SPAN></I></B><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Principal, W2AGZ Technologies</FONT></SPAN></B><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Visiting Scholar, Applied Physics, Stanford (2005-2008)</FONT></SPAN></B><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">EPRI Science Fellow (Retired)</FONT></SPAN></B><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">IBM Research Staff Member Emeritus</FONT></SPAN></B><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><A HREF="mailto:w2agz@pacbell.net"><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">w2agz@pacbell.net</FONT></SPAN></B><SPAN LANG="en-us"></SPAN></A><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><A HREF="http://www.w2agz.com/"><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B></B></SPAN><B><SPAN LANG="en-us"></SPAN></B><B><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">http://www.w2agz.com</FONT></SPAN></B><SPAN LANG="en-us"></SPAN></A><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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