Dear Ibrahim I checked the structure with xcrysden and it seems correct to me, thus we can rule out the usually main reason for bad scf convergence. :-) However there are still a few thing you should try to adjust:
1) celldm(1)=5.9722904441d0, celldm(3)=15.8777369953d0, celldm(3) is too small. you have a thick slab (~40 A) and a very thin vacuum space between periodically repeated images (~10 A). You have therefore a strong interaction along z between the images, and this is not only a source of instability, but also a bad practice when you want to investigate surface properties. You should consider *at least* a vacuum space between slabs as large as the slab itself. And decoupling the images by using one of the possible approaches (e.g., assume_isolated='esm'; esm_bc='bc1') can be also useful in the case of a strong dipole along z. 2) mixing_beta=0.7d0 This is the default value. In difficult cases you should lower it down to 0.1, or even to 0.01 in *very* difficult cases. 3) smearing='mv', A 'gaussian' smearing generally yields a more stable algorithm. You can optimize your system and then restart the calculation with a different smearing scheme, if you are sure you need it. 4) vdw_corr='grimme-d2', This is not directly related with your convergence issue, as DFT-D2 is a semiempirical plug-in independent of density or wavefunctions. But it is well known that it overbinds metal-containing slabs. You should try (maybe starting with a MoS2 bilayer) to evaluate the effect of different schemes, such as rVV10 or c09-vdw-df, on the structural and electronic properties of your slab. 5) ecutwfc=60, The value is quite high for US pseudopotentials. If you are sure you need such an accurate basis set you might consider the use of NC pseudopotentials. ONCV PPs should be a very good choice: a wfc cutoff a bit higher (80 Ry) but a density cutoff quite lower (320 Ry), and no overhead with the US augmentation charge... HTH Giuseppe Quoting Ibrahim Yahaya Muhammad <[email protected]>: > Dear all, > I am trying to perform a 'vc-relax' calculation for seven layers MoS2. But > convergence not achieved. I increase electron_maxstep to 1000 still > convergence not achieved. > Please find attached, the input and output. > > Best Regards, > > Ibrahim Yahaya Muhammad GIUSEPPE MATTIOLI CNR - ISTITUTO DI STRUTTURA DELLA MATERIA Via Salaria Km 29,300 - C.P. 10 I-00015 - Monterotondo Scalo (RM) Mob (*preferred*) +39 373 7305625 Tel + 39 06 90672342 - Fax +39 06 90672316 E-mail: <[email protected]> _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
