Dear Tim,
quick comment - does the CP constant of motion stay flat (econt - electronic energy plus ionic kinetic plus ficititious kinetic) ? If it does, you have a properly executed CP simulation, where, depending on the gap, you observe some amount of "equilibration" between the real (ions) and fictitious degrees of freedom. I forgot if the 2x1 in C is slighlty metallic - of course, molten Si is definitely metallic, so it all seems to make sense. If the case, have a close look at the Hutter Marx paper review we often mention, and available on the web. If the drift is small, you can add a thermostat on ions (and maybe also on electrons, to avoid them warming up). If the drift is large, you need to move to born-oppenheimer simulations, of which cp has the "ensemble-dft" recipe. If you do that, remember that only the current cvs (and not the public release) has a fix for an important bug in parallel calculations. nicola Tim Teatro wrote: > 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) > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- --------------------------------------------------------------------- Prof Nicola Marzari Department of Materials Science and Engineering 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu