Dear all,
I am carrying out high pressure NPT MD simulations using cp.x for a system
I am working on. As these simulations are being done for long times they
require multiple restarts. While restarting a simulation, I noticed that
there is a discontinuity in the fictitious K.E in the new simulation. I
started looking into this when, in a particular simulation, there was a
very large discontinuity of fictitious K.E (more than 10 meV/atom) on
restart and this caused large fluctuation in other parameters such as the
enthalpy. The following is a plot of the same (The restart step is marked
with a vertical line).
When I further investigated several other simulations, I observed that a
discontinuity in fictitious K.E occurs whenever a simulation is restarted,
although in most cases the magnitude of such discontinuity is negligible.
Therefore, it went unnoticed previously. An example is shown below:
However, in some cases, the magnitude of this discontinuity is higher,
which causes sudden fluctuations in the same and dies down very fast as
below:
It can be seen that the magnitude of the discontinuity here is very low
compared to the first case. I haven't yet identified the cause of the same
and am unsure whether such a discontinuity is to be expected whenever there
is a restart. It would be really helpful if someone has an insight on this
issue. Also, I would appreciate some help to get an idea on how I can
proceed to investigate whether the above behaviour would have affected the
dynamics and if so by how much.
The relevant part of the cp.x restart input file is shown below for
reference:
&control
title = 'mol',
calculation = 'vc-cp',
restart_mode = 'restart',
ndr = 77,
ndw = 78,
dt = 5.0d0,
nstep = 100000,
iprint = 5,
isave = 100,
etot_conv_thr = 1.0D-8,
forc_conv_thr = 1.0D-5,
ekin_conv_thr = 1.0D-8,
tstress = .true.,
tprnfor = .true.,
prefix = 'mol',
outdir = './',
pseudo_dir = '/home/rashidr/pseud/',
verbosity = 'medium',
max_seconds = 258700,
/
&system
ibrav = 0,
celldm(1) = 15.54772162,
ntyp = 4,
nat = 80,
ecutwfc = 62,
ecutrho = 480,
occupations="fixed",
vdw_corr= 'grimme-d2'
nr1b = 30,
nr2b = 30,
nr3b = 30,
ecfixed = 80,
qcutz = 150,
q2sigma = 2.0,
/
&electrons
electron_dynamics = 'verlet',
emass = 200.d0,
emass_cutoff = 1.d0,
electron_velocities = 'default',
electron_maxstep = 2000,
conv_thr = 1.0D-10,
electron_temperature = 'not_controlled',
/
&ions
ion_dynamics = 'verlet',
ion_temperature = 'nose',
tempw= 300.0,
fnosep = 55.0,
ion_velocities = 'default',
ion_positions = 'default',
/
&cell
cell_dynamics = 'pr',
cell_parameters = 'default'
cell_velocities = 'default'
press = 400.0,
/
Any help regarding the above would be appreciated.
Thanks and Regards,
Rashid Rafeek
PhD student
Department of Chemistry
IISER Bhopal
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