<div>Dear All,</div>
<div> Hope everyone is having a great Holiday. would you please help me out with this, I'm looking for the "ev.f" that help to calculate the bulk modulus of a material. But I couldn't find it any where, please let me know where and how I can find that and use it to calculate for the bulk modulus, B.</div>
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<div>Thank you so much,</div>
<div>Tram Bui<br><br></div>
<div class="gmail_quote">On Tue, Dec 7, 2010 at 1:14 AM, Sandro Scandolo <span dir="ltr"><<a href="mailto:scandolo@ictp.it">scandolo@ictp.it</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">In the specific case of the O2 molecule, in a molecular orbital picture<br>O2 has two degenerate pi-star HOMO orbitals that need to be filled with<br>
2 electrons. The ground state is a triplet S=1 (up,up),<br>(up,down)+(down,up),(down,down), the next state is a singlet<br>(up,down)-(down,up). A good representation of the triplet should be<br>given by the ground state of a spin-polarized calculation. The ground<br>
state should have nup-ndown=2, and the two unpaired electrons fill the<br>two pi-star orbitals (with the same spin). I believe you don't need to<br>impose any symmetry to find this ground state. If you force the system<br>
to have total spin=0 (in a spin-polarized calculation), you should<br>obtain the state (up,down) (or its degenerate counterpart (down,up)).<br>This state does not satisfy the correct symmetry of the 2-electron wfc,<br>so in principle does not correspond to any of the correct many-electron<br>
states above. However this spurious state can be expressed as a linear<br>combination (sum or difference) of one of the triplet states<br>((up,down)+(down,up)) and the singlet state ((up,down)-(down,up)).<br>Perhaps its energy corresponds to the average energy of the triplet and<br>
the singlet??!?<br><br>Best regards<br>Sandro<br>
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<div class="h5"><br><br>On 06/12/2010 09:45, Stefano de Gironcoli wrote:<br>> Nicola Marzari wrote:<br>>> I've never managed to get from anyone, including some of the luminaries<br>>> in the fundamentals of DFT, a clear answer to which solution is the<br>
>> "correct" one. Note that even with nosym=.true. you ahve the option<br>>> of having occupation 2.0 on 2 of the p orbitals, or occupation<br>>> 1.3333333 on oeach of the 3 p orbitals - the latter solution<br>
>> would probably be similar to the symmetrized solution (but shouldn't<br>>> be identical).<br>>><br>> I think there's no general consensus whether it's "more correct" to have<br>
> the lowest possible energy giving up the known symmetry of the true GS<br>> or to constraint the system to the expected symmetry accepting a<br>> slightly higher energy... Of course the "true" xc functional would not<br>
> put you in this dilemma, but while awaiting for it, I think the<br>> important thing is to be aware of the two alternatives and clearly state<br>> which one one chooses to conpare with.<br>><br>> stefano<br>
><br>><br>><br>>> nicola<br>>><br>>><br>>><br>>> On 12/3/10 5:27 PM, <a href="mailto:elbuesta@icqmail.com">elbuesta@icqmail.com</a> wrote:<br>>><br>>>> Dear all,<br>
>>><br>>>> I recently evaluated with PW the binding energy of a O2 molecule using<br>>>> the regular ultra-soft PP from the webpage. I noticed that the energy<br>>>> obtained could be 5.7eV or 6.7eV depending if the flag "nosym=.true." is<br>
>>> used or not in the energy evaluation of the isolated oxygen atom. I<br>>>> would like to know if anyone could help me understand why such a large<br>>>> difference is obtained for this system, since for many other systems<br>
>>> (such as metals) the inclusion of "nosym=.true." for the isolated atom<br>>>> do not affect so much (or not at all) the value of the binding/cohesive<br>>>> energy.<br>>>><br>
>>><br>>>> Thanks very much for your time, and all best for all!<br>>>><br>>>> Fabio Negreiros<br>>>> IPCF - CNR, Pisa - Italia<br>>>><br>>><br>>><br>> _______________________________________________<br>
> Pw_forum mailing list<br>> <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>> <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
><br><br></div></div><font color="#888888">--<br>Sandro Scandolo -- http:/<a href="http://www.ictp.it/~scandolo" target="_blank">www.ictp.it/~scandolo</a><br></font>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Tram Bui<br><br>B.S. Materials Science & Engineering<br><a href="mailto:trambui@u.boisestate.edu">trambui@u.boisestate.edu</a><br><br>