DFT-Cohesive energy is decided by the functional and the pseudo-potential. If the pseudo-potential and the functional predict correctly the ground state of isolated atom and the bulk, we usually get less than 10% error. This is the case of Al with GGA (I believe). For some other, especially in transition metal where the ground states of isolated atoms (and/or bulks) are not well predicted within DFT, the error in cohesive energy could be 20% or more. When a pseudo-potential is generated, it must be well tested before releasing. It's safe to use.
On Wed, Sep 16, 2009 at 2:19 AM, udayagiri sai babu <udayagiri3 at gmail.com>wrote: > Dear PWSCF users > I calculated the cohesive energy for aluminium using GGA potential, which > came out to be 3.59 ev/atom. When i compared this value with that of given > in Kittel (3.34ev/atom) the error is 7.5%. Here i would like to know how > much error in cohesive energy is acceptable and also if somebody can comment > on error tolerance in lattice parameter and Bulk modulus (for GGA as well as > LDA) as well it would be nice. > Thanks in advance > > -- > U.Saibabu > PhD student, > Deformation mechanisms modeling group, > Materials engineering department, > IISc Bangalore, > India. > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- -------------------------------------------------- Duy Le PhD Student Department of Physics University of Central Florida. --00163646be844c72110473da595f Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable <div>From my understanding, correct me if I am wrong.</div><div><br></div>D= FT-Cohesive energy is decided by the functional and the pseudo-potential. I= f the pseudo-potential and the functional predict correctly the ground stat= e of isolated atom and the bulk, we usually get less than 10% error. This i= s the case of Al with GGA (I=A0believe). For some other, especially in tran= sition metal where the ground states of isolated atoms (and/or bulks) are n= ot well predicted within DFT, the error in cohesive energy could be 20% or = more.<div> <br></div><div>When a pseudo-potential is generated, it must be well tested= before releasing. It's safe to use.<br><br><div class=3D"gmail_quote">= On Wed, Sep 16, 2009 at 2:19 AM, udayagiri sai babu <span dir=3D"ltr"><<= a href=3D"mailto:udayagiri3 at gmail.com">udayagiri3 at gmail.com</a>></span> = wrote:<br> <blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p= x #ccc solid;padding-left:1ex;">Dear PWSCF users<br>I calculated the cohesi= ve energy for aluminium using GGA potential, which came out to be 3.59 ev/a= tom. When i compared this value with that of given in Kittel (3.34ev/atom) = the error is 7.5%. Here i would like to know how much error in cohesive ene= rgy is acceptable and also if somebody can comment on error tolerance in la= ttice parameter and Bulk modulus (for GGA as well as LDA) as well it would = be nice.<br> Thanks in advance<br clear=3D"all"><font color=3D"#888888"><br>-- <br>U.Sai= babu<br>PhD student,<br>Deformation mechanisms modeling group,<br>Materials= engineering department,<br>IISc Bangalore,<br>India.<br> </font><br>_______________________________________________<br> Pw_forum mailing list<br> <a href=3D"mailto:Pw_forum at pwscf.org">Pw_forum at pwscf.org</a><br> <a href=3D"http://www.democritos.it/mailman/listinfo/pw_forum"; target=3D"_b= lank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br> <br></blockquote></div><br><br clear=3D"all"><br>-- <br>-------------------= -------------------------------<br>Duy Le<br>PhD Student<br>Department of P= hysics<br>University of Central Florida.<br> </div> --00163646be844c72110473da595f--
