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)