<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd"><html><head><meta name="qrichtext" content="1" /><style type="text/css">p, li { white-space: pre-wrap; }</style></head><body style=" font-family:'Arial'; font-size:10pt; font-weight:400; font-style:normal;">Dear Vega<br>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p>> Do the both calculation output the singlet state energy?<br>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p>They are two different states: <br>
'spin=2, multiplicity=1' --> Here you can deal with a system with two, spatially different, single-electron KS wavefunctions, occupied by one 'up' electron and one 'down' electron. This can be called an "open shell singlet" You could find that: a) your total magnetization is 0.00 mB, because this is forced by the 'multiplicity=1' keyword, but your absolute magnetization could be, say, 2.00 mB, a sort of antiferromagnetic system; b) the energy difference with a real triplet, in this case, could be almost negligible, so that the system could be considered a triplet forced in this state due to the 'multiplicity=1' constraint<br>
'spin=1' --> Here you are forcing a restricted representation of your system, that is, you have KS wavefunctions that can be occupied by a couple of paired electrons.<br>
Which is the 'best' singlet? You should know, depending upon the properties of your system.<br>
Hope this help<br>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p>Giuseppe<br>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p>On Wednesday 13 January 2010 11:11:14 vega lew wrote:<br>
> Dear sir,<br>
><br>
> Do the both calculation output the singlet state energy?<br>
> If I want to compare the energy difference of singlet and triplet, which<br>
> calculated singlet state energy should be used?<br>
><br>
> thank you for your help.<br>
><br>
> best wishes,<br>
><br>
> vega<br>
><br>
> On 1/13/2010 14:43, Paolo Giannozzi wrote:<br>
> > On Jan 13, 2010, at 6:41 , vega lew wrote:<br>
> >> I have compare the results of two calculation for singlet state<br>
> >> with or without the option 'spin=2, multiplicity=1'.<br>
> ><br>
> > they aren't the same. A non-polarized calculation will yield S^2=0,<br>
> > Sz=0.<br>
> > A spin-polarized calculation with "multiplicity=1" will yield Sz=0<br>
> > but not<br>
> > necessarily S^2=0. See for instance J. Phys. Chem. B 105, 11227<br>
> > (2001) for a nice description of how neglecting to appreciate such<br>
> > difference may lead to unphysical results.<br>
> ><br>
> > P.<br>
> > ---<br>
> > Paolo Giannozzi, Dept of Physics, University of Udine<br>
> > via delle Scienze 208, 33100 Udine, Italy<br>
> > Phone +39-0432-558216, fax +39-0432-558222<br>
> ><br>
> ><br>
> ><br>
> > _______________________________________________<br>
> > Pw_forum mailing list<br>
> > Pw_forum@pwscf.org<br>
> > http://www.democritos.it/mailman/listinfo/pw_forum<br>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p><p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br></p>-- <br>
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