[Pw_forum] cp.x temperature decreases

[Tim Teatro]

Hello All,

Thank you in advance for your time and any help you can offer.

We are running on HP/XC clusters, Opteron CPUs and pathscale
compilers, MPI, etc. The clusters have version 3.2.3 of the
Quantum-ESPRESSO code.

We are experiencing an issue with two MD simulations using cp.x in
certain atomic systems. The two systems of note are a C(111) 2x1 slab
type structure (12 layers with 96 atoms), and the other is a simple
cubic 64 atom Si system. The problem is that over a 40 000 time step
run, there is a very noticeable decrease in average temperature. Of
course, the temperature oscillates over the run, but the C111 system
appears to have decreasing temperature over time (from about 800K to
about 600K for example). The temperature is not controlled and thermal
motion is achieved by initial random displacement of atoms within the
run (using the tranp switch). At the end of this e-mail, I will attach
the set of input files used in the run. It appears that the rate of
energy loss is related to the energy of the system. A system which at
a higher temperature appears to lose energy more quickly. For C111,
over 40 000 time steps, this visually resembles a linear decrease, but
as I mention in a moment, the Si system suggests that the relationship
is exponential.

The Si system seems to lose temperature in a way that resembles
(visually) an exponential decrease. The temperature eventually levels
off after falling from some initial value. This only appears to happen
at higher temperatures (I've only seen it in one of my colleagues
runs, and the temperature was above 1500K)

Sixty-four atom GaAs, which has the same structure as Si, shows a very
stable temperature.

Best regards,


Timothy A.V Teatro

--
Timothy A.V. Teatro <timothy.teatro at uoit.ca>
University of Ontario Institute of Technology
Faculty of Science
2000 Simcoe Street North
Oshawa, ON, CANADA, L1H 7K4


Input files for C(111) 2x1 (96 atom, 12 layer slab)_________________
**************************************************************

&control
title = 'c96 GS',
calculation='cp',
restart_mode='from_scratch',
prefix='c96',
outdir = '/scratch/timtro/c96/'
ndr = 51,
ndw = 51,
dt = 5.0,
nstep = 100,
isave=100,
tprnfor=.TRUE.,
forc_conv_thr=1.0d-3,
etot_conv_thr = 1.d-6,
ekin_conv_thr = 1.d-5,
wf_collect=.TRUE.,
/
&system
ibrav = 8,
celldm(1)=16.510372468,
celldm(2)=0.577350269,
celldm(3)=2.558782523,
nat=96,
ntyp=1,
xc_type = 'BLYP',
ecutwfc = 30.0,
ecutrho = 300.0,
/
&electrons
emass=400.d0,
emass_cutoff=2.5d0,
electron_dynamics='cg',
/
&ions
ion_positions='default',
ion_velocities='zero',
ion_dynamics='none'
/
ATOMIC_SPECIES
 C   12.0107  C.pz-vbc.UPF
ATOMIC_POSITIONS (bohr)
...



&control
title = 'c96 SD',
calculation='cp',
restart_mode='restart',
prefix='c96',
outdir = '/scratch/timtro/c96/'
ndr = 51,
ndw = 51,
dt = 5.0,
nstep = 500,
isave=100,
tprnfor=.TRUE.,
forc_conv_thr=1.0d-6,
etot_conv_thr = 1.d-6,
ekin_conv_thr = 1.d-5,
wf_collect=.TRUE.,
/
&system
ibrav = 8,
celldm(1)=16.510372468,
celldm(2)=0.577350269,
celldm(3)=2.558782523,
nat=96,
ntyp=1,
xc_type = 'BLYP',
ecutwfc = 30.0,
ecutrho = 300.0,
/
&electrons
emass=400.d0,
emass_cutoff=2.5d0,
electron_dynamics='sd',
electron_velocities='zero',
/
&ions
ion_positions='default',
ion_velocities='zero',
ion_dynamics='none'
/
ATOMIC_SPECIES
 C   12.0107  C.pz-vbc.UPF
ATOMIC_POSITIONS (bohr)
...


&control
title = 'c96 RAND',
calculation='cp',
restart_mode='restart',
prefix='c96',
outdir = '/scratch/timtro/c96/'
ndr = 51,
ndw = 51,
dt = 5.0,
nstep = 100,
isave=100,
tprnfor=.TRUE.,
forc_conv_thr=1.0d-6,
etot_conv_thr = 1.d-6,
ekin_conv_thr = 1.d-5,
wf_collect=.TRUE.,
/
&system
ibrav = 8,
celldm(1)=16.510372468,
celldm(2)=0.577350269,
celldm(3)=2.558782523,
nat=96,
ntyp=1,
xc_type = 'BLYP',
ecutwfc = 30.0,
ecutrho = 300.0,
/
&electrons
emass=400.d0,
emass_cutoff=2.5d0,
electron_dynamics='sd',
electron_velocities='zero',
/
&ions
ion_positions='default',
ion_dynamics='none',
tranp(1)=.TRUE.,
amprp(1)=0.42898,
/
ATOMIC_SPECIES
 C   12.0107  C.pz-vbc.UPF
ATOMIC_POSITIONS (bohr)
...


&control
title = 'c96 MD',
calculation='cp',
restart_mode='reset_counters',
prefix='c96',
outdir = '/scratch/timtro/c96/'
ndr = 51,
ndw = 51,
dt = 5.0,
nstep = 40000,
isave=200,
tprnfor=.TRUE.,
forc_conv_thr=1.0d-6,
etot_conv_thr = 1.d-6,
ekin_conv_thr = 1.d-5,
wf_collect=.TRUE.,
/
&system
ibrav = 8,
celldm(1)=16.510372468,
celldm(2)=0.577350269,
celldm(3)=2.558782523,
nat=96,
ntyp=1,
xc_type = 'BLYP',
ecutwfc = 30.0,
ecutrho = 300.0,
/
&electrons
emass=400.d0,
emass_cutoff=2.5d0,
electron_dynamics='verlet',
electron_velocities='zero',
/
&ions
ion_positions='default',
ion_dynamics='verlet',
ion_velocities='zero',
/
ATOMIC_SPECIES
 C   12.0107  C.pz-vbc.UPF
ATOMIC_POSITIONS (bohr)