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Dear sir,<br><br>Thank you for responding<br>> please note that convergence parameters can be _very_ arbitrary<br>> between different codes and they can be in very strange units.<br><br>sure, I think I have convert the units properly. I want to use 1.0e-5 eV/atom as the CASTEP do<br>for my Energy convergence. Do you think I should multiple 12 for my cell has 12 atoms? Maybe <br>I did it wrong...<br><br>> before going any further with running big calculations. try<br>> smaller ones.<br><br>I think it's small enough. It can be finished within an hour.<br><br>> and have you checked the requirements for each <br>> pseudopotential? is your stress tensor converged wrt. wavefunction <br>> _and_ density cutoff? ...and k-points? you are using vanderbilt <br>> ultrasoft pseudopotentials and they can require unexpectedly high <br>> density cutoffs. <br><br>Many piece of works published on journals said 25 and 200 Ryd is enough.<br>I'll test a 400 eV ( 30 Ryd ) later.<br><br>> if i remember correctly. you are also not mentioning <br>> whether the reference you are comparing to is using the _same_ <br>> functional that you are using. different functionals <br>> tend to over/underestimate lattice parameters differently.<br><br>Here is part of the reference: J. Phys. Chem. B 2006, 110, 7463-7472<br><br>Calculations were carried out in the framework of density functional theory by using <br>the Vienna ab-initio simulation package (VASP). Ultrasoft pseudopotentials were used to<br>describe the ionic cores, and a plane-wave basis set with a cutoff energy of 400 eV <br>was used to expand the valence electrons. The nonlocal exchange and correlation <br>energies were calculated with the Perdew-Wang (PW91) functional of the generalized<br>gradient approximation (GGA). Calculations including spinpolarization have been performed <br>for all structures presented here. The results were compared with those from non-spinpolarized<br>calculations in the case of a zero magnetic moment. The consistence of the results from<br>both calculations ensures that the system is in a true nonmagnetic state. The geometries<br>were relaxed using a conjugate-gradient or quasi-Newton scheme as implemented in VASP.<br>The atomic structures were relaxed until the forces on all unconstrained atoms were less<br>than 0.03 eV/Å. Similar setups have been employed in the study of a wide range of systems<br>including metal and metal-oxide surfaces by the authors and many others. <br><br>The calculated bulk anatase TiO2 lattice parameters a = b = 3.803 A, c = 9.603 A, c/a = 2.525, <br>which agree well with the experiments, were used to construct the periodic slabs for<br>the (101) surface calculations. .............<br><br>Also other literatures, such as Journal of Molecular Structure (Theochem) 709 (2004) 73–78.<br><br>As the above paragraph in literature said, what kind of pseudopotentials should be used?<span class="EC_grigio"></span>Ti.pw91-nsp-van.UPF ?<br>Or <span class="EC_grigio"></span>Ti.pw91-sp-van_ak.UPF? Or Ti.pbe-sp-van_ak.UPF <span class="EC_grigio">?</span><br><br>I note that in castep the corresponding name of pseudopotentials are O_00PBE.usp, Ti_00PBE.usp. <br>But there is another option for us to choose x-c functional. While QE 4.0 doesn't has, QE read from<br> pseudopotential files. So Ti.pbe-xxxxx.UPF and O.pbe-xxx.UPF maybe not suitable. <span style="text-decoration: underline;"><span style="text-decoration: underline;"></span></span>What do you think<br>witch is more suitable for calculation described by the reference?<br><br><pre>By the way, I note that CASTEP has find 32 symmetry operations of my cell. My cell is <br>a standard anatase crystall. But Q-E only can find 4 at most since I adjust parameters of <br>~/espresso-4.0/PW/eqvect.f90. Do this matter effect my results significantly?<br></pre><br><br><br><font size="4"><span style="font-family: Lucida Handwriting,Cursive;">Vega Lew</span></font><br>PH.D Candidate in Chemical Engineering<br>
State Key Laboratory of Materials-oriented Chemical Engineering<br>College of Chemistry and Chemical Engineering<br>Nanjing University of Technology, 210009, Nanjing, Jiangsu, China<br><br><font size="4"><span style="font-family: Lucida Handwriting,Cursive;"><br></span></font><a href="http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline" target="_blank"></a>
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