[Wien] volume optimization and force minimization
and imaging to study the structure of matter. ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter. ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- next part -- An HTML attachment was scrubbed... URL: http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20100225/63c97315/attachment.htm
[Wien] Bad formation energies for the charged vacancies
Thank you for the replies. I thought that such a correction was already done in Wien2k. I should have noticed the warning in case.scf0 file: :WARN :CHARGED CELL with -1.000 an energy correction like C Q**2/(L eps) is not included (PRB51,4014; PRB73,35215) I'm not sure if I understand it correctly: 1. The value of V_0 is written in case.scf0 file and is marked as VCOUL-ZERO for each atom. So, should one take the sum of VCOUL-ZERO of all the atoms? 2. As V_0 is arbitrarily defined, one should make some reference calculation and use the potential difference V_0(q)-V_0_ref, right?. So, is the problem that the shift which corresponds to zero is different for the different charge states and we cannot just take the value of V_0 from the neutral cell as the reference? Or, will the calculation for an empty cell (0 electrons) be such a reference? with kind regards, Yurko On 24 February 2010 22:58, Laurence Marks L-marks at northwestern.edu wrote: Did you try (from one of Freeman's papers I believe): -Q*V_0(Q)/2 where Q is the excess charge of the cell (-ve for a negative cell) and V_0(Q) is the vacuum Coulomb potential in the calculation which is a function of Q which will depend upon the RMT. Note the factor of 2. I don't think this is in Wien2k at the moment, it needs to be added retroactively (or could in principle be added to the code). It is a long time ago and I seem to remember that this worked for the empty cell test, but no longer have the data, so On Wed, Feb 24, 2010 at 3:18 PM, Peter Blaha pblaha at theochem.tuwien.ac.at 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 Natanzonyurko.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
[Wien] Bad formation energies for the charged vacancies
Dear Prof. Blaha, I have another question on the topic. Does this problem also affect the other quantities such as electron density, DOS and forces? If I need to perform a geometric optimization after I have added a charge, should I also apply the correction to the forces in order to get the correct ground state? 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] problem with DOS calculations
Dear Wien2k users, I am trying to calculate DOS for a surface supercell but I am not sure why case.dos1evup file shows only zeros in the columns for density of states. I have calculated DOS many times before without any problem for bulk system. In my surface calculation I have used MPI version of wien2k and have only one k-point. I have used the following steps as usual, x lapw2 -c -qtl -p -up x lapw2 -c -qtl -p -dn edited case.int file x tetra -up x tetra -dn I have tried different range of energies in case.int file but couldn't make it work. I would appreciate if anyone can tell me how to solve this problem or whether there is a problem in calculating DOS for only one k-point. Thanks, Fhokrul _ Hotmail: Trusted email with powerful SPAM protection. https://signup.live.com/signup.aspx?id=60969 -- next part -- An HTML attachment was scrubbed... URL: http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20100225/df629fba/attachment.htm
[Wien] problem with DOS calculations
Dear Fhokrul, With only one k-point you should only have a discrete set of energies. Therefore I think the DOS would be a set of delta functions. Your energy resolution in case.int is unlikely to capture them. Best, David. Md. Fhokrul Islam wrote: Dear Wien2k users, I am trying to calculate DOS for a surface supercell but I am not sure why case.dos1evup file shows only zeros in the columns for density of states. I have calculated DOS many times before without any problem for bulk system. In my surface calculation I have used MPI version of wien2k and have only one k-point. I have used the following steps as usual, x lapw2 -c -qtl -p -up x lapw2 -c -qtl -p -dn edited case.int file x tetra -up x tetra -dn I have tried different range of energies in case.int file but couldn't make it work. I would appreciate if anyone can tell me how to solve this problem or whether there is a problem in calculating DOS for only one k-point. Thanks, Fhokrul Hotmail: Trusted email with powerful SPAM protection. Sign up now. https://signup.live.com/signup.aspx?id=60969 ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- David A. Tompsett Quantum Matter Group Cavendish Laboratory J. J. Thomson Avenue Cambridge CB3 0HE U.K. Tel: +44 7907 566351 (mobile) Fax: +44 1223 768140 http://www-qm.phy.cam.ac.uk/
[Wien] problem with DOS calculations
Hi David, Thanks for your quick reply. In my calculations I have thousands of energies (the basis size in my calculations was about 16000) and so I thought if I adjust dE in case.int then I should be able to capture those energies even if I use only one k-point. For example say at gamma point there are ten energies within 1 eV of Fermi level and if I set my window in case.int file within that range, I should be able to see this number in case.dos file. I have tried different energy range and dE values but case.dos file in all cases show zeros in the column for total DOS. Is my argument right? Thanks again, Fhokrul Date: Thu, 25 Feb 2010 13:38:51 + From: dat36 at cam.ac.uk To: wien at zeus.theochem.tuwien.ac.at Subject: Re: [Wien] problem with DOS calculations Dear Fhokrul, With only one k-point you should only have a discrete set of energies. Therefore I think the DOS would be a set of delta functions. Your energy resolution in case.int is unlikely to capture them. Best, David. Md. Fhokrul Islam wrote: Dear Wien2k users, I am trying to calculate DOS for a surface supercell but I am not sure why case.dos1evup file shows only zeros in the columns for density of states. I have calculated DOS many times before without any problem for bulk system. In my surface calculation I have used MPI version of wien2k and have only one k-point. I have used the following steps as usual, x lapw2 -c -qtl -p -up x lapw2 -c -qtl -p -dn edited case.int file x tetra -up x tetra -dn I have tried different range of energies in case.int file but couldn't make it work. I would appreciate if anyone can tell me how to solve this problem or whether there is a problem in calculating DOS for only one k-point. Thanks, Fhokrul Hotmail: Trusted email with powerful SPAM protection. Sign up now. https://signup.live.com/signup.aspx?id=60969 ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- David A. Tompsett Quantum Matter Group Cavendish Laboratory J. J. Thomson Avenue Cambridge CB3 0HE U.K. Tel: +44 7907 566351 (mobile) Fax: +44 1223 768140 http://www-qm.phy.cam.ac.uk/ ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien _ Your E-mail and More On-the-Go. Get Windows Live Hotmail Free. https://signup.live.com/signup.aspx?id=60969 -- next part -- An HTML attachment was scrubbed... URL: http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20100225/2575f4be/attachment.htm
[Wien] problem with DOS calculations
I believe that as currently structured the utility programs for analyzing the dos only work for more than one k-point. In principle it should not be too hard to wade through the code, see where it is getting confused if there is only one k-point, and change the code slightly so it will do some reasonable broadening. This would certainly be useful. Peter does an amazing job with Wien2k, but he cannot do everything and still enjoy life (e.g. go skiing). Since Wien2k is somewhat of a community project, maybe someone would volunteer to do the above 2010/2/25 Md. Fhokrul Islam fislam at hotmail.com: Hi David, ??? Thanks for your quick reply. In my calculations I have thousands of energies (the basis size in my calculations was about 16000) and so I thought if I adjust dE in case.int then I should be able to capture those energies even if I use only one k-point. For example say at gamma point there are ten energies within 1 eV of Fermi level and if I set my window in case.int file within that range, I should be able to see this number in case.dos file. I have tried different energy range and dE values but case.dos file in all cases show zeros in the column for total DOS. Is my argument right? Thanks again, Fhokrul Date: Thu, 25 Feb 2010 13:38:51 + From: dat36 at cam.ac.uk To: wien at zeus.theochem.tuwien.ac.at Subject: Re: [Wien] problem with DOS calculations Dear Fhokrul, With only one k-point you should only have a discrete set of energies. Therefore I think the DOS would be a set of delta functions. Your energy resolution in case.int is unlikely to capture them. Best, David. Md. Fhokrul Islam wrote: Dear Wien2k users, I am trying to calculate DOS for a surface supercell but I am not sure why case.dos1evup file shows only zeros in the columns for density of states. I have calculated DOS many times before without any problem for bulk system. In my surface calculation I have used MPI version of wien2k and have only one k-point. I have used the following steps as usual, x lapw2 -c -qtl -p -up x lapw2 -c -qtl -p -dn edited case.int file x tetra -up x tetra -dn I have tried different range of energies in case.int file but couldn't make it work. I would appreciate if anyone can tell me how to solve this problem or whether there is a problem in calculating DOS for only one k-point. Thanks, Fhokrul Hotmail: Trusted email with powerful SPAM protection. Sign up now. https://signup.live.com/signup.aspx?id=60969 ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- David A. Tompsett Quantum Matter Group Cavendish Laboratory J. J. Thomson Avenue Cambridge CB3 0HE U.K. Tel: +44 7907 566351 (mobile) Fax: +44 1223 768140 http://www-qm.phy.cam.ac.uk/ ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien Your E-mail and More On-the-Go. Get Windows Live Hotmail Free. Sign up now. ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter.
[Wien] problem with DOS calculations
Addendum: you can take the intermediate output, put them into a spreadsheet such as Excel and plot the dos yourself with some broadening -- it works but is not so convenient. On Thu, Feb 25, 2010 at 8:44 AM, Laurence Marks L-marks at northwestern.edu wrote: I believe that as currently structured the utility programs for analyzing the dos only work for more than one k-point. In principle it should not be too hard to wade through the code, see where it is getting confused if there is only one k-point, and change the code slightly so it will do some reasonable broadening. This would certainly be useful. Peter does an amazing job with Wien2k, but he cannot do everything and still enjoy life (e.g. go skiing). Since Wien2k is somewhat of a community project, maybe someone would volunteer to do the above 2010/2/25 Md. Fhokrul Islam fislam at hotmail.com: Hi David, ??? Thanks for your quick reply. In my calculations I have thousands of energies (the basis size in my calculations was about 16000) and so I thought if I adjust dE in case.int then I should be able to capture those energies even if I use only one k-point. For example say at gamma point there are ten energies within 1 eV of Fermi level and if I set my window in case.int file within that range, I should be able to see this number in case.dos file. I have tried different energy range and dE values but case.dos file in all cases show zeros in the column for total DOS. Is my argument right? Thanks again, Fhokrul Date: Thu, 25 Feb 2010 13:38:51 + From: dat36 at cam.ac.uk To: wien at zeus.theochem.tuwien.ac.at Subject: Re: [Wien] problem with DOS calculations Dear Fhokrul, With only one k-point you should only have a discrete set of energies. Therefore I think the DOS would be a set of delta functions. Your energy resolution in case.int is unlikely to capture them. Best, David. Md. Fhokrul Islam wrote: Dear Wien2k users, I am trying to calculate DOS for a surface supercell but I am not sure why case.dos1evup file shows only zeros in the columns for density of states. I have calculated DOS many times before without any problem for bulk system. In my surface calculation I have used MPI version of wien2k and have only one k-point. I have used the following steps as usual, x lapw2 -c -qtl -p -up x lapw2 -c -qtl -p -dn edited case.int file x tetra -up x tetra -dn I have tried different range of energies in case.int file but couldn't make it work. I would appreciate if anyone can tell me how to solve this problem or whether there is a problem in calculating DOS for only one k-point. Thanks, Fhokrul Hotmail: Trusted email with powerful SPAM protection. Sign up now. https://signup.live.com/signup.aspx?id=60969 ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- David A. Tompsett Quantum Matter Group Cavendish Laboratory J. J. Thomson Avenue Cambridge CB3 0HE U.K. Tel: +44 7907 566351 (mobile) Fax: +44 1223 768140 http://www-qm.phy.cam.ac.uk/ ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien Your E-mail and More On-the-Go. Get Windows Live Hotmail Free. Sign up now. ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter. -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter.
[Wien] Bad formation energies for the charged vacancies
I think the forces are going to be OK, the issue is a constant energy correction for the nominal background charge. Since this should be constant, I don't think it will contribute at all to forces which depend upon gradients. On Thu, Feb 25, 2010 at 6:07 AM, Yurko Natanzon yurko.natanzon at gmail.com wrote: Dear Prof. Blaha, I have another question on the topic. Does this problem also affect the other quantities such as electron density, DOS and forces? If I need to perform a geometric optimization after I have added a charge, should I also apply the correction to the forces in order to get the correct ground state? 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 Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter.
[Wien] problem with DOS calculations
Addendum: you can take the intermediate output, put them into a spreadsheet such as Excel and plot the dos yourself with some broadening -- it works but is not so convenient. Two comments on this: 1) you can specify a broadening in case.int (see Sec. 8.1.3 of the UG) 2) there is a very robust integration of the DOS plotted in case.outputt. Even if the energy step is too large to see a spike, it will appear clearly as a sudden jump of the integrated value. Stefaan
[Wien] Bad formation energies for the charged vacancies
As mentioned before, the potential (and thus the density) should be ok. With respect to forces I'd suggest you run a simple test. Take a simple compound which has forces, charge it, and compare the forces and the total energy. You can test it even better by taking eg. your GaN, reduce the symmetry and displace the two atoms against each other (put N at .25-d,.25-d,.25-d; where d is a small value (ranging from eg. 0.03 to -0.03 in steps of 0.01). Calculate the total energy as function of displacement and compare with the forces I have another question on the topic. Does this problem also affectthe other quantities such as electron density, DOS and forces? If Ineed to perform a geometric optimization after I have added a charge,should I also apply the correction to the forces in order to get thecorrect ground state? with kind regards,Yurko -- Yurko (aka Yuriy, Iurii, Jurij etc) NatanzonPhD studentDepartment for Structural Research (NZ31)Henryk Niewodnicza?ski Institute of Nuclear PhysicsPolish Academy of Sciencesul. Radzikowskiego 152,31-342 Krakow, PolandE-mail: Yurii.Natanzon at ifj.edu.pl, yurko.natanzon at gmail.com___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] problem with DOS calculations
Does it work for 1 k-point? On Thu, Feb 25, 2010 at 10:28 AM, Stefaan Cottenier Stefaan.Cottenier at ugent.be wrote: Addendum: you can take the intermediate output, put them into a spreadsheet such as Excel and plot the dos yourself with some broadening -- it works but is not so convenient. Two comments on this: 1) you can specify a broadening in case.int (see Sec. 8.1.3 of the UG) 2) there is a very robust integration of the DOS plotted in case.outputt. Even if the energy step is too large to see a spike, it will appear clearly as a sudden jump of the integrated value. Stefaan ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Chair, Commission on Electron Crystallography of IUCR www.numis.northwestern.edu/ Electron crystallography is the branch of science that uses electron scattering and imaging to study the structure of matter.
[Wien] problem with DOS calculations
I guess we had these questions before. The TETRAHEDRON method calculates the DOS band by band. With one k-point a band consists only of ONE energy and thus would give a delta function. In other words: even if your eigenvalues are at 0.09 (band 1) and 0.11 (band 2), the DOS from tetra at 0.1 is exactly zero (while the integrated DOS (see Stefaans comment) will increase by 2 electrons for the energies 0.099 and 0.100. For one k-point, one needs a histogramm method, i.e. you should specify an energy mesh (eg. 0.005 Ry), then take case.energy (or case.qtl) and then simply count the eigenvalues in each interval (remember, the DOS is the number of states/energy intervall). Finally you may smoothen the curve and put some gauss broadening on it. Stefaan Cottenier schrieb: Addendum: you can take the intermediate output, put them into a spreadsheet such as Excel and plot the dos yourself with some broadening -- it works but is not so convenient. Two comments on this: 1) you can specify a broadening in case.int (see Sec. 8.1.3 of the UG) 2) there is a very robust integration of the DOS plotted in case.outputt. Even if the energy step is too large to see a spike, it will appear clearly as a sudden jump of the integrated value. Stefaan ___ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://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] Bad formation energies for the charged vacancies
Dear Peter,
Yes, the background charge must be taken into account as part of the
net-neutral total charge in order to have well-defined total energy.
Then as long as the compensation charge is then in exactly the same
way as the remaining physical charge (i.e., enters all the same
integrals), then the arbitrary constant in potential should not matter
since:
\int{ \rho (V + c)} = \int{ \rho V} + c \int{ \rho} = \int {\rho V},
independent of arbitrary constant c.
John
On Feb 24, 2010, at 11:54 PM, Peter Blaha wrote:
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.)
Yes, this is the question and yes, of course we add a positive or
negative background.
We are quite confident that the resulting potential is ok, but the
question is if there
is a correction to the total energy due to the background charge.
I believe: yes (something like Q * V-col_average / 2), but my
problem is that V-coul
is in an infinite crystal only known up to an arbitrary constant and
thus this correction
is arbitrary.
--
-
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
-
___
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[Wien] Bad formation energies for the charged vacancies
Dear Prof. Blaha and Prof. Marks, Thank you for your replies. I'm afraid about the following thing: the Markove-Payne-like (Phys. Rev. B 51, 4014) correction you propose should cancel the error which exists due to the repulsion of charged defects in the periodic crystal and results in some constant energy shift. However, the problem is that the values of formation energy are not just shifted to some constant, but have the OPPOSITE signs: If we add the correction for e.g. Mg, it will be 0.245-V_0/2 for +1 charge and -0.199+V_0/2 for the -1 charge In the Plane-Wave code which I used for comparison, the Payne-Markov corrections to the total energy is NOT applied and the values are: -0.226 Ry for +1 charge and 0.281 for -1 charge Then, it is unlikely that the addition or substracting V_0 will change the signs of both formation energies (unless V_0 also changes its sign for +1 and -1 charge states). Could it be that the problem lies somewhere else? with best regards, Yurko On 25 February 2010 17:19, Laurence Marks L-marks at northwestern.edu wrote: I think the forces are going to be OK, the issue is a constant energy correction for the nominal background charge. Since this should be constant, I don't think it will contribute at all to forces which depend upon gradients. -- 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] Bad formation energies for the charged vacancies
In the integrals below, \rho is just the electronic charge density (without
nuclei).
Thus c \int{\rho] does NOT vanish and gives c * NE (number of electrons).
However, if rho comes from electronic states, each eigenvalue is shifted by the
constant c
and thus the sum of eigenvalues cancels the c * NE term above.
However, when I add a background charge to neutralize the unit cell, this
does not come
from any eigenvalue, so if I handle this in the usual way, \rho will now
integrate to
NE + Q, and I get an extra c * Q term, which is not compensated by an
eigenvalue.
PS: In response to another posting, since Q is +1 and -1 (and we assume that
V-could does not change
too much), the corrections would have opposite sign for the positively and
negatively charged cell !!
John Pask schrieb:
Dear Peter,
Yes, the background charge must be taken into account as part of the
net-neutral total charge in order to have well-defined total energy.
Then as long as the compensation charge is then in exactly the same way
as the remaining physical charge (i.e., enters all the same
integrals), then the arbitrary constant in potential should not matter
since:
\int{ \rho (V + c)} = \int{ \rho V} + c \int{ \rho} = \int {\rho V},
independent of arbitrary constant c.
John
On Feb 24, 2010, at 11:54 PM, Peter Blaha wrote:
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.)
Yes, this is the question and yes, of course we add a positive or
negative background.
We are quite confident that the resulting potential is ok, but the
question is if there
is a correction to the total energy due to the background charge.
I believe: yes (something like Q * V-col_average / 2), but my problem
is that V-coul
is in an infinite crystal only known up to an arbitrary constant and
thus this correction
is arbitrary.
--
-
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
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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
-
