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<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman">Dear wien users,</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman"> <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman">I am calculating the optical conductivity of bcc iron<SPAN style="mso-spacerun: yes"> </SPAN>and found that the absorptive part is not always positive. This means that a plot of Re_sigma_xx<SPAN style="mso-spacerun: yes"> </SPAN>Re_sigma_yy<SPAN style="mso-spacerun: yes"> </SPAN>Re_sigma_zz<SPAN style="mso-spacerun: yes"> </SPAN>using<SPAN style="mso-spacerun: yes"> </SPAN>file fe.absorpup has a negative part between 2.7eV and about 14.0eV. I think this is strange. This is because the mathematical _expression (per spin) for<SPAN style="mso-spacerun: yes"> </SPAN>Re_sigma_xx<SPAN style="mso-spacerun: yes"> </SPAN>etc. makes it impossible for it to be negative.<SPAN style="mso-spacerun: yes"> </SPAN></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman"></FONT></SPAN> </P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman"><o:p></o:p></FONT></SPAN> </P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman">Thanks.</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman"> <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN lang=EN-GB><FONT face="Times New Roman">C M I Okoye</FONT></SPAN></P></DIV></TD></TR></TBODY></TABLE></DIV></DIV></TD></TR></TBODY></TABLE></DIV></DIV></TD></TR>
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<P><FONT face=courier>Chukwu<STRONG>emeka</STRONG> M I Okoye</FONT></P>
<P><FONT face=courier>Department of Physics and Astronomy,</FONT></P>
<P><FONT face=courier>University of Nigeria,Nsukka,</FONT></P>
<P><FONT face=courier>Enugu State, <STRONG>Nigeria</STRONG>.</FONT></P>
<P><FONT face=courier>+2348045257257</FONT></P>
<P><FONT face=courier>+234 42 771611</FONT></P></TD></TR>
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