[Pw_forum] help

[Ari P Seitsonen]

Dear Anik shrivastava,

   I do not fully understand your questions, but small comments: So far as 
I remember the system of eight atoms of silicon is not stable in the 
diaomd structure if using only the Gamma point; this might thus lead to 
an increase of the ionic temperature. If the ionic temperature is very 
high, like 6000 K, the system is probably metallic and a fractional 
occupation should be used (and possibly a smaller 'mixing_beta').

   I would start by trying to increase the size of the system or the number 
of k points - preferably the former, as that would lead to a bit more 
physical dynamics. I would also try reducing the value of 'delta_t', as 
400 K sounds quite a lot to me.

     Greetings from Zurich,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Institut für Chemie der Universität Zürich, CH-8057 Zürich
   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935


On Wed, 11 Jun 2014, Anik Shrivastava wrote:

> Dear all
> The program mentioned below is for heating and quenching of cooling, i have
> some question regarding this, please tell me what mistake am i doing.
> 
> 1This system doesn't quench and show higher temperature at the end,say
> initial temp is 1600K and, End temperature is around 6000K, when is using
> 'reduced-T' ,and around 2500K when berendsen is used, except these two, if i
> use any different way i.e rescaling etc. then system would not be converge,
> why?
> 
> 2.If i choose deltaT and nraise less than 400 and 20 respectively then
> system doesn't converge ????
> 
> 
> Thanks in advance
> 
> &control
> calculation='md'
> restart_mode='from_scratch',
> prefix = 'Si'
> pseudo_dir = '/home/metal/Desktop/espresso-5.0.2/pseudo',
> outdir='./',
> dt=10,
> nstep=500,
> disk_io='high'
> /
> &system
> ibrav= 1, celldm(1)=10.18, nat= 8, ntyp= 1,
> ecutwfc = 35.0, nosym=.true.
> /
> &electrons
> conv_thr = 1.0d-8,
> mixing_beta = 0.7
> 
> /
> &ions
> ion_dynamics='verlet'
> pot_extrapolation='second-order'
> wfc_extrapolation='second-order'
> ion_temperature='reduce-T'
> tempw=1600.D0
> delta_t=-400.D0
> nraise=20
> 
> /
> ATOMIC_SPECIES
> Si 28.086 Si.pz-vbc.UPF
> 
> Si -0.123 -0.123 -0.123
> Si 0.377 0.377 -0.123
> Si 0.377 -0.123 0.377
> Si -0.123 0.377 0.377
> Si 0.123 0.123 0.123
> Si 0.623 0.623 0.123
> Si 0.623 0.123 0.623
> Si 0.123 0.623 0.623
> K_POINTS {automatic}
> 1 1 1 0 0 0
> 
> 
> 
> Anik shrivastava
> Senior Research Fellow
> Naval Materials Research Lab,DRDO
> Mumbai-400085
> India
> 
>