Dear QE users and developers, 1 When dealing with orthorhombic systems, I start with space_group super-tight relaxation of the atomic positions (keeping right balance in force and scf accuracy, increasing ecutrho plus 100 Ry than my system actually requires, etc), continue with vc-relax using dofree = ibrav (and press_thr = 0.0), and Always obtain at least one lattice constant screwed up (with an error like +/- 0.1 A as compared to the experimental constant). I tried 1000 setups for a few systems (varying functionals, vdw corrections, different pseudo libraries, etc) and have a feeling that sth is not right with vc-relax: for other than orthorhombic systems the results match the experimental lattice constants with an acceptable error.
2 I was wondering how vc-relax work for big orthorhombic unit cells. I took alpha-S8 (space group 70, so 128 atoms turn into 32 within ibrav = 10 with 8 symmetry elements) and am not satisfied with any lattice constants: on PBEsol level, error in volume is <1% as compared to the experimental unit cell, but lattice constants are like 10.602 (exp: 10.465), 12.937 (exp: 12.866), 24.286 (exp: 24.486) A that do not look acceptable at all :-( I would hugely appreciate any comments, Thanks, Alex. ___ Aleksandra Oranskaia (M.Sc.) ChemS PhD student, KAUST Phone: +966 50 1335254 -- This message and its contents, including attachments are intended solely for the original recipient. If you are not the intended recipient or have received this message in error, please notify me immediately and delete this message from your computer system. Any unauthorized use or distribution is prohibited. Please consider the environment before printing this email.
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