On Fri, 4 Jul 2008, vega lew wrote: VL> > Think about, why you set etot_conv_thr so tight (don't mix it up with VL> > conv_thr, which seemed to be sloppy for this calculation ), while you set VL> > forc_conv_thr to be really sloppy? (Btw, is there any reason to set the VL> > cutoffs/thresholds to such precision?) VL> VL> Many litterature doing so. The force threshold is usually set as 0.03eV and 0.05eV VL> for larger system. the cutoff in literature can be 380 or 400eV sometimes. VL> I'm only doing repeat work and learning how to do a perfect calculation. VL> Also the conv_thr and etot_conv_thr is taken from CASTEP calculation directly. Others
please note that convergence parameters can be _very_ arbitrary between different codes and they can be in very strange units. VL> doing so of the same system is the only reason. I'm a beginner of VL> PWscf and DFT calculation. So I think doing repeat work of others VL> and discuss with skilled people may be the best way for me. What I'm VL> doing now is something more like a homework rather than the research VL> work. I'm learning to using PWscf. Thank you for your help. before going any further with running big calculations. try smaller ones. and have you checked the requirements for each pseudopotential? is your stress tensor converged wrt. wavefunction _and_ density cutoff? ...and k-points? you are using vanderbilt ultrasoft pseudopotentials and they can require unexpectedly high density cutoffs. if i remember correctly. you are also not mentioning whether the reference you are comparing to is using the _same_ functional that you are using. different functionals tend to over/underestimate lattice parameters differently. cheers, axel. VL> VL> VL> Vega Lew VL> PH.D Candidate in Chemical Engineering VL> VL> State Key Laboratory of Materials-oriented Chemical Engineering VL> College of Chemistry and Chemical Engineering VL> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China VL> VL> VL> VL> _________________________________________________________________ VL> Connect to the next generation of MSN Messenger? VL> http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline -- ======================================================================= Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu Center for Molecular Modeling -- University of Pennsylvania Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323 tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425 ======================================================================= If you make something idiot-proof, the universe creates a better idiot.
