Dear Marks, Thanks for your reply. you gave nice explanation. I will apply in my system to solve the problem. Regards, Santhy jaiker Laurence Marks <L-marks at northwestern.edu> wrote: Let me try and explain a little. In general you want to have the RMT's as large as possible because then the calculations converge faster and also this is a better model for the core electrons. The RMT's that you need to have don't track with classic atomic radii but more what is going on with the core electrons, for instance for transition metals you generally want to have a larger RMT than for oxygen. What RMT you use also depends upon which states you decide to treat as semi-core, i.e. where you set the cutoff between core and valence in lstart (and case.inc, case.in1, case.in2).
The Wien code cannot do a calculation if RMT's overlap. During minimization, often atoms will move quite close to each other, for instance if one wants to move to a very different position relative to the first. In this case you need to have a much smaller RMT than you would use for the optimized atomic positions. The command "setrmt" will do this approximately for you. It is only a computer code, so you should look at what it is recommending, think about the values and run some tests (e.g. a simpler bulk structure) to understand what different RMT's mean. You should also look at the value of :NEC in case.scf and also the core integrals in case.outputm to check that you have adequately constrained the core electrons within the muffin-tins. No computer code is foolproof, the user has to make sensible decisions. When you are running a minimization, you want to set things up with your "best guess" as to how close the atoms are going to come during the minimization. If you think your starting point is very close to the minimized positions, you can use a small reduction; if you think you are far you may want to use a larger one. If you err with too much reduction this is not too large a problem; if you use too little the minimization won't run properly and you will have to adjust the RMT's (see the clminter command). The standard way I run a minimization is to make a guess at the reduction, make the RMT's a bit smaller than this, use a smaller RKMAX (e.g. RKMAX/min(RMT)=2.5 to 3) and a smaller oversampling in case.in0, less k-points and less stringent convergence parameters (e.g. -fc 4 not -fc 1). Only when the forces have reduced down to some reasonable level (e.g. 6-10 mRyd/au) do I change to more accurate values. The value of "2" in nn is not particularly important, it is just how far out the code prints out neighbors. On Wed, Jul 2, 2008 at 6:21 AM, Santhy Jaiker wrote: > Dear wien2k users, > i have some basic doubts in % reduction of RMT. Any suggestion will be > appreciated. > ? What is role of 'RMTreduction' in mini? > ? What are the factors decides the %reduction of RMT? > ? what is the minimum and maximum % reduction of RMT? > ? nn distance i.e distance factor is usually 2. Is it applicable to > all the cases? > Thank is advance > > Regards, > Santhy jaiker > > Regards, > Santhy Jaiker > > Research Scholar, > Materials Thermodynamics Lab, > Department of Metallurgical and Materials Engineering, > Indian Institute of Technology Madras, > Chennai - 600 036, India > Tel: 91-044-22575763 > ********************************************** > A truly happy person is one > who can enjoy the scenery on a detour > ********************************************** > > ________________________________ > Bring your gang together. Do your thing. Find your favourite Yahoo! Group. > _______________________________________________ > 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 Commission on Electron Diffraction of IUCR www.numis.northwestern.edu/IUCR_CED _______________________________________________ Wien mailing list Wien at zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien Regards, Santhy Jaiker Research Scholar Materials Thermodynamics Lab Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras Chennai - 600 036 India Tel: 91-044-22575763 ********************************************** A truly happy person is one who can enjoy the scenery on a detour ********************************************** --------------------------------- Download prohibited? No problem. CHAT from any browser, without download. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20080703/75583b47/attachment.html
