Dear Venkataramana,
At least a couple of problems:
- This is not a cluster, this is a crystal: There is no vacuum what so
ever around the two atoms
- ... but the k point sampling is for an isolated system: Bulk silicon
with only Gamma point is a disaster
- If you use 'nosym = .false.' (the default) you have practically no
degrees of freedom, except the translations that are (to my knowledge) not
taken into account. Thus the atoms can only vibrate along the
direction [111], due to the inversion symmetry the two atoms are even more
coupled
- The value for 'ecutwfc' is too low to obtain accurate forces
- Convergence threshould would be too loose
- 'scf_must_converge = .false.' is asking for even more trouble
Besides that, I admit that I have little experience about the Langevin
dynamics, what are good values for the friction term etc. But like you
see, this is fully unphysical "dynamics" already. Please try to clarify
first if you indeed want to simulate a cluster or bulk.
Greetings from Zurich,
apsi
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
Ari Paavo Seitsonen / ari.p.seitso...@iki.fi / http://www.iki.fi/~apsi/
Ecole Normale Supérieure (ENS), Département de Chimie, Paris
Mobile (F) : +33 789 37 24 25(CH) : +41 79 71 90 935
On Fri, 14 Aug 2015, Venkataramana Imandi wrote:
Dear all,
I am using quantum espresso (version:5.1.2) for doing Langevin dynamics on
silicon cluster (total atoms: 2) running on Red Hat machine with serial and
parallel process. If I
don't use "nosym=.true." keyword in the input file, the following error is observed,
which is shown below. If I use "nosym=.true." keyword, then super cell is blowing during
Langevin dynamics. Moreover, the coordinates of individual silicon atoms is
merging in the output file, which is shown below for one of the snapshot during
Langevin dynamics.
The distance between two Silicon atoms is increasing and at the end of 70 md
steps the distance is 1152 angstroms. Kindly suggest me what is region behind
in the error. I am new
user and not well aware of Langevin dynamics in the quantum espresso software
package. Input file and coordinates of one of the snapshot are attached.
%%
Error in routine checkallsym (1):
some of the original symmetry operations not satisfied
%%
calculation='md',
dt=20.D0,
nstep=100,
etot_conv_thr=1.0D-5,
forc_conv_thr=1.0D-4,
prefix='si_lang' ,
pseudo_dir='/home/venkat/ORR1/PPS1'
/
ibrav= 2,
celldm(1)=10.18,
nat=2,
ntyp= 1,
ecutwfc = 8.0,
nosym=.true.
/
electron_maxstep=2000,
diagonalization='david',
conv_thr = 1.0e-5,
mixing_beta = 0.3,
scf_must_converge=.false.
/
pot_extrapolation = 'second_order',
wfc_extrapolation = 'second_order',
ion_dynamics='langevin',
refold_pos=.true.
tempw=300.D0,
nraise=2
/
ATOMIC_SPECIES
Si 28.086 Si.pz-vbc.UPF
ATOMIC_POSITIONS {alat}
Si -0.123 -0.123 -0.123
Si 0.123 0.123 0.123
K_POINTS {automatic}
1 1 1 0 0 0
one snapshot during Langevin dynamics
ATOMIC_POSITIONS (alat)
Si 210.463044756 215.584817447-144.659285586
Si -210.463044756-215.584817447 144.659285586
Best,
Venkataramana
PhD student
IIT Bombay
___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum
