[Pw_forum] Silicon 111 surface

[Giovanni Cantele]

1) the atomic positions are likely wrong, I cannot understand what is the system you want to calculate. For example, the Si-In distance is 1.1 A, that looks
very small. Try to look at your structure, opening the input file with XCrysDen. It is worth, before performing any further calculation, to check whether it is EXACTLY what you want.


2) in the case you would like to simulate the Si(111) SURFACE in the presence of In, your input does not correspond to a surface calculation. There is not vacuum space
introduced between periodic replicas of the same slab, and there is k-point sampling in the direction orthogonal to the surface. If instead you are studying something like
a Si heterostructure (e.g. a superlattice), please disregard this point

3) you are using ultra soft pseudo potential, the ecutwfc is likely too high (this however does not give convergence issues, but can make your calculation much slower
than needed!). On the other hand, you are not setting the ecutrho variable, that by default is 4*ecutwfc. For ultrasoft pseudo potentials, as you might learn reading
the relevant literature on the subject, a higher charge density cut-off is required, usually from 6 to 12 times ecutwfc

4) to improve convergence, increasing degauss might help, for systems very difficult to converge (but even in this case you should be aware of what degauss is and how to use it)
and also decrease mixing_beta to 0.3, or 0.1 or maybe even less


Giovanni



> On 23 Feb 2017, at 06:59, Ubaid Mohd <onlymubaid at gmail.com> wrote:
> 
> Hi,
> 
> I am trying to scf calculation of silicon(111)_Indium  and the total force on the atom is not converging. Initially, the scf cycle itself was not converging.
> What is wron with my input file.
> Thanx,
> Ubaid
> 
> 
> 
> 
> Input File
> 
> 
> &CONTROL
>   calculation='scf',
>   outdir='Pwscf',
>   prefix='Si_In',
>   pseudo_dir='.',
>   verbosity='low',
> /
> 
> &SYSTEM
>   ibrav=0,
>   celldm(1)=7.2565749368d0,
>   nat=7,
>   ntyp=2,
>   ecutwfc=90,
>   input_dft='PBE',
>   occupations='smearing',
>   smearing='mv',
>   degauss=0.005d0,
> /
> 
> &ELECTRONS
>   conv_thr=1d-06,
>   mixing_beta=0.7d0,
> /
> 
> ATOMIC_SPECIES
>   In 114.818000d0 In.pbe-d-rrkjus.UPF
>   Si  28.085500d0 Si.pbe-n-rrkjus_psl.0.1.UPF
> 
> ATOMIC_POSITIONS {crystal}
>   Si   0.1708493746d0   0.3787081237d0   0.2302895286d0
>   Si   0.8375160412d0   0.7120414570d0   0.3136228619d0
>   Si   0.8375160412d0   0.7120414570d0   0.5636228619d0
>   Si   0.5041827079d0   1.0453747903d0   0.6469561953d0
>   Si   0.5041827079d0   1.0453747903d0   0.8969561953d0
>   Si   0.1708493746d0   0.3787081237d0   0.9802895286d0
>   In   0.2708493746d0   0.4787081237d0   0.3397104714d0
> 
> K_POINTS {automatic}
>  5 5 5 0 0 0
> 
> CELL_PARAMETERS {alat}
>   1.000000000000d0  0.000000000000d0  0.000000000000d0
>   -0.500000000000d0  0.866025403784d0  0.000000000000d0
>   0.000000000000d0  0.000000000000d0  2.449489742783d0
> 
> 
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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