Dear Peter, Is the question regarding the computation of total energy per unit cell in an infinite crystal with non-neutral unit cells? If so, then the total energy diverges -- and so is not well-defined. (So neutralizing backgrounds must be added in such cases to obtain meaningful results, etc.)
John On Feb 24, 2010, at 1:18 PM, Peter Blaha wrote: > I've started some tests after the first query and it seems we might > miss a term in the total > energy. > > I created a clmsum-file (density) which is constant and is > normalized to one and put this into > a cell with a single H nucleus. > So it refers to the test case of a H+ ion in a lattice, where I do > not add a constant background, but > put the "background charge into case.clmsum. > > When one switches off the XC-terms, the resulting E-tot contains the > integral (rho *V-coul) and since > rho is constant (equal to Q/volume), we get the average potential in > the unit cell (not only the > interstital, where it is zero anyway) multiplied by the constant rho). > > This term is missing when I put a clmsum file with rho=zero, but add > a "background charge" > by case.inm, while the resulting potentials are identical for the > two methods. > > However, for a charged bulk system there is still a big problem, > because V-coul is determined > only up to a constant and is shifted arbitrarily such that the > potential in the interstital is zero. > In "neutral" calculations such a shift does not matter, since it > will be canceled by the sum of > eigenvalues, but when adding the constant background it matters. > > Thus, this correction term depends on RMT ? > > At the moment I'm not sure how I should continue. I think in other > codes such a correction is > added, but as mentioned, I guess the correction depends on the > arbitrary choice of V-zero. > > > Laurence Marks schrieb: >> Please see the next email on the list:http:// >> *zeus.theochem.tuwien.ac.at/pipermail/wien/2007-January/008713.html >> I think this is right and you take V0 from case.output0 (it is >> printedthere). You should do an empty cell test (no electrons) to >> verify thisand the units of V0, perhaps also looking at the code >> itself -- andremember to check the limit as the distance between >> atoms gets large. >> On Wed, Feb 24, 2010 at 11:05 AM, Yurko Natanzon<yurko.natanzon at gmail.com >> > wrote:> Dear Wien2k users and developers,> I'd like to refresh >> the discussion about the total energies of the> charged cells which >> took place three years ago:> http://*zeus.theochem.tuwien.ac.at/ >> pipermail/wien/2007-January/008711.html>> I'm trying to calculate >> the formation energy of the Hydrogen vacancy> in +/-1 charge states >> and find that the results are bad (much differ> from the >> literature) although the formation energy of the neutral> hydrogen >> vacancy is good. So my question arises if we can trust the> values >> of the total energies for the charged cells in the recent> version >> of Wien2k?>> To investigate this issue further I have performed the >> following> tests: I've done the calculations of the total energy of >> Mg, MgH2 and> GaN for three cases: neutral cell, cell with one >> electron removed (+1> charge) and a cell with an electron added (-1 >> charge). The results> were compared with the same calculati > on with another plane-wave code> and are the following:> > -----------------------------------------> hcp Mg:> Wien2k:> E(+1)- > E(0) = 0.245 Ry> E(-1)-E(0) = -0.199 Ry>> Plane-Wave code:> E(+1)- > E(0) = -0.226 Ry> E(-1)-E(0) = 0.281 Ry>> bcc MgH2> Wien2k:> E(+1)- > E(0) = 0.277 Ry> E(-1)-E(0) = 0.085 Ry>> Plane-Wave code:> E(+1)- > E(0) = 0.024 Ry> E(-1)-E(0) = 0.326 Ry>> fcc GaN> Wien2k:> E(+1)- > E(0) = 1.12 Ry> E(-1)-E(0) = -0.717 Ry>> Plane-Wave code:> E(+1)- > E(0) = -0.151 Ry> E(-1)-E(0) = 0.443 Ry> > ------------------------------------------------->> In wien2k the > charged cell was created by changing the number of> electrons in > case.in2 and adding the corresponding background charge> in > case.inm. One can observe, that the energies have the same order of> > magnitude, but the sequence of energies E(+1), E(0) and E(1) is> > inverse. It seems, that the system with +1 charge (electron > removed)> behaves like the system with -1 charge in the Plane-Wave > code. Of> course, the results of tests are no > t physical, because no supercell> was used and no geometric > relaxation was performed (however, it is not> needed for Mg), but if > one tries to do all the supercell and> relaxation stuff and tries to > calculate the defect formation energy,> the result will be the > same.>> I'd be grateful if you comment on this and suggest any > corrections> which should be provided to the total energies for the > charged cells.>> with kind regards,> Yurko>>> --> Yurko (aka Yuriy, > Iurii, Jurij etc) Natanzon> PhD student> Department for Structural > Research (NZ31)> Henryk Niewodnicza?ski Institute of Nuclear > Physics> Polish Academy of Sciences> ul. Radzikowskiego 152,> 31-342 > Krakow, Poland> E-mail: Yurii.Natanzon at ifj.edu.pl, yurko.natanzon at > gmail.com > > _______________________________________________> Wien mailing > list> Wien at zeus.theochem.tuwien.ac.at> http:// > *zeus.theochem.tuwien.ac.at/mailman/listinfo/wien> >> -- Laurence MarksDepartment of Materials Science and EngineeringMSE >> Rm 2036 Cook Hall2220 N Campus DriveNorthwestern >> UniversityEvanston, IL 60208, USATel: (847) 491-3996 Fax: (847) >> 491-7820email: L-marks at northwestern dot eduWeb: >> www.*numis.northwestern.eduChair, Commission on Electron >> Crystallography of IUCRwww.*numis.northwestern.edu/Electron >> crystallography is the branch of science that uses >> electronscattering and imaging to study the structure of >> matter._______________________________________________Wien mailing listWien >> at zeus.theochem.tuwien.ac.athttp >> ://*zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > -- > ----------------------------------------- > Peter Blaha > Inst. Materials Chemistry, TU Vienna > Getreidemarkt 9, A-1060 Vienna, Austria > Tel: +43-1-5880115671 > Fax: +43-1-5880115698 > email: pblaha at theochem.tuwien.ac.at > ----------------------------------------- > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://*zeus.theochem.tuwien.ac.at/mailman/listinfo/wien