[CPMD-list] temperature Drift in CPMD
Axel Kohlmeyer
akohlmey at cmm.chem.upenn.edu
Wed Oct 3 19:46:34 CET 2007
On Wed, 3 Oct 2007, Samir H. Mushrif wrote:
hello samir,
SM> I have a system with 210 atoms (C, H, O and Pd, 596 electrons) at 500 K
SM> and I equilibrated the system using TEMPCONTROL IONS option in CPMD.
SM> After ~1000 MD steps (a cycle of a couple of hundred MD steps followed
SM> by wavefunction optimization and QUENCH ELECTRONS, preserving the ionic
SM> velocities using GEOMETRY file) I observed that the EKS is not drifting
SM> and is oscillating around a mean value. The EKINC was observed to be
SM> approximately 0.14. I used this value of EKINC and shifted to NOSE IONS
SM> MASSIVE. But now when I run my simulation, I observed that the TEMP
SM> keeps decreasing and it goes upto 300 K in the first 70 MD steps. Am I
SM> doing something wrong here or shall I wait for some more time (probably
SM> a few hundred MD steps) to see the trend since it is too early to
SM> conclude that something is going wrong here.
it looks like it will take a long time to bring your system
to equilibrium. since TEMPCONTROL only rescales all velocities,
it does not take care of equipartitioning of the vibrational
modes. so i would recommend you keep running with your system
as is and wait. there still seems to be a drift in EKS and it
may take a while until you get there. it may help to switch back
to TEMPCONTROL for a while and then go back again to NOSE ION MASSIVE.
at your current stage, i would not put a thermostat on the electrons,
as you are then 'blind' for when your wavefunction is slowly degrading
and when it would be better to do another QUENCH BO ELECTRONS.
please always keep in mind, that 1000 steps of MD are not much,
specifically at a time step as short as you need it for CP dynamics.
if you have a tricky system and start far from equilibrium, it
can easily take you of the order of 10ps worth of trajectory to
get you to the point where you can have meaningful simulations.
one trick to get there faster would be to start equilibration
at a slightly higher target temperature and then cool down,
instead of slowly heating up to your final target. but then
you run the risk of destroying more delicate structures, that
you may want to preserve (and which you then would have to
protect with constraints).
as you may have noticed by now, doing a good CPMD calculation needs
as much craftmanship and practice as it requires an understanding
of the related theory and methods. ... and since it combines electron
structure theory and molecular dynamics (= statistical mechanics),
you are subject to problems in both areas.
just be patient and keep watching your output and system carefully.
cheers,
axel.
SM>
SM> My input file looks as follows:
SM>
SM> &CPMD
SM> MOLECULAR DYNAMICS CP
SM> RESTART WAVEFUNCTION COORDINATES CELL GEOFILE
SM> TEMPERATURE
SM> 500.0
SM> NOSE IONS MASSIVE
SM> 500.0 1800.0 ************
SM> Since I have a system with polyaromatic hydrocarbons, I took the
SM> frequency of a C-C bond vibration as the characteristic frequency for
SM> NOSE IONS
SM> ************
SM> NOSE ELECTRONS
SM> 0.14 10000.0
SM> LSD
SM> MAXSTEP
SM> 1000
SM> TRAJECTORY XYZ SAMPLE FORCES
SM> 5
SM> TIMESTEP
SM> 4.0
SM> EMASS
SM> 600.0
SM> FILEPATH
SM> /home/grad/samir/prod1/
SM> MEMORY BIG
SM> &END
SM> .
SM> .
SM> .
SM> .
SM>
SM> Relevant part of my output file is as follows:
SM>
SM> NFI EKINC TEMPP EKS ECLASSIC EHAM
SM> DIS TCPU
SM> 1 0.00034 490.7 -861.96227 -859.89980 -859.89946
SM> 0.210E-04 940.27
SM> 2 0.00434 470.2 -861.94521 -859.90271 -859.89837
SM> 0.827E-04 954.48
SM> 3 0.01558 443.0 -861.92918 -859.91403 -859.89845
SM> 0.182E-03 945.44
SM> 4 0.03282 414.1 -861.91762 -859.93137 -859.89854
SM> 0.314E-03 930.96
SM> 5 0.05239 387.2 -861.91034 -859.95102 -859.89862
SM> 0.476E-03 974.99
SM> 6 0.07124 364.1 -861.90615 -859.96993 -859.89870
SM> 0.664E-03 936.85
SM> 7 0.08761 345.5 -861.90387 -859.98635 -859.89873
SM> 0.875E-03 940.03
SM> 8 0.10087 331.2 -861.90274 -859.99964 -859.89877
SM> 0.111E-02 939.76
SM> 9 0.11075 320.8 -861.90204 -860.00955 -859.89881
SM> 0.136E-02 933.02
SM> 10 0.11724 313.6 -861.90113 -860.01607 -859.89882
SM> 0.162E-02 943.45
SM> 11 0.12060 309.0 -861.89964 -860.01943 -859.89883
SM> 0.191E-02 944.31
SM> 12 0.12125 306.4 -861.89737 -860.02006 -859.89881
SM> 0.221E-02 968.37
SM> 13 0.11983 305.3 -861.89451 -860.01862 -859.89879
SM> 0.253E-02 957.94
SM> 14 0.11702 305.3 -861.89137 -860.01578 -859.89876
SM> 0.287E-02 935.75
SM> 15 0.11344 306.3 -861.88831 -860.01217 -859.89873
SM> 0.323E-02 929.10
SM> 16 0.10963 307.8 -861.88561 -860.00835 -859.89872
SM> 0.361E-02 960.17
SM> 17 0.10596 309.7 -861.88341 -860.00467 -859.89871
SM> 0.401E-02 938.94
SM> 18 0.10269 311.7 -861.88174 -860.00140 -859.89871
SM> 0.443E-02 945.02
SM> 19 0.09991 313.7 -861.88054 -859.99863 -859.89872
SM> 0.487E-02 950.65
SM> 20 0.09763 315.6 -861.87965 -859.99636 -859.89872
SM> 0.533E-02 955.43
SM> 21 0.09584 317.1 -861.87894 -859.99457 -859.89873
SM> 0.581E-02 935.81
SM> 22 0.09447 318.3 -861.87828 -859.99319 -859.89873
SM> 0.632E-02 935.46
SM> 23 0.09345 319.1 -861.87757 -859.99217 -859.89872
SM> 0.684E-02 929.06
SM> 24 0.09270 319.5 -861.87676 -859.99142 -859.89872
SM> 0.739E-02 954.78
SM> 25 0.09216 319.7 -861.87586 -859.99087 -859.89871
SM> 0.795E-02 937.35
SM> 26 0.09178 319.6 -861.87490 -859.99048 -859.89870
SM> 0.854E-02 941.61
SM> 27 0.09153 319.5 -861.87396 -859.99022 -859.89869
SM> 0.915E-02 974.73
SM> 28 0.09140 319.3 -861.87313 -859.99008 -859.89868
SM> 0.977E-02 938.41
SM> 29 0.09140 319.2 -861.87253 -859.99007 -859.89867
SM> 0.104E-01 942.28
SM> 30 0.09152 319.3 -861.87222 -859.99018 -859.89866
SM> 0.111E-01 943.61
SM> 31 0.09176 319.7 -861.87227 -859.99041 -859.89866
SM> 0.118E-01 938.72
SM> 32 0.09208 320.3 -861.87268 -859.99074 -859.89865
SM> 0.125E-01 935.33
SM> 33 0.09246 321.3 -861.87344 -859.99111 -859.89865
SM> 0.132E-01 952.80
SM> 34 0.09284 322.5 -861.87449 -859.99149 -859.89865
SM> 0.139E-01 945.53
SM> 35 0.09315 324.0 -861.87575 -859.99180 -859.89865
SM> 0.147E-01 940.43
SM> 36 0.09336 325.8 -861.87715 -859.99201 -859.89865
SM> 0.154E-01 955.35
SM> 37 0.09343 327.8 -861.87862 -859.99208 -859.89865
SM> 0.162E-01 945.36
SM> 38 0.09337 329.9 -861.88012 -859.99202 -859.89865
SM> 0.170E-01 947.16
SM> 39 0.09322 332.2 -861.88163 -859.99187 -859.89864
SM> 0.179E-01 942.03
SM> 40 0.09303 334.5 -861.88315 -859.99167 -859.89864
SM> 0.187E-01 957.14
SM> 41 0.09287 336.8 -861.88469 -859.99151 -859.89863
SM> 0.196E-01 968.58
SM> 42 0.09279 339.0 -861.88625 -859.99142 -859.89863
SM> 0.205E-01 969.97
SM> 43 0.09284 341.2 -861.88784 -859.99147 -859.89863
SM> 0.214E-01 949.84
SM> 44 0.09304 343.1 -861.88943 -859.99167 -859.89863
SM> 0.224E-01 979.63
SM> 45 0.09340 344.9 -861.89098 -859.99202 -859.89863
SM> 0.233E-01 956.39
SM> 46 0.09389 346.4 -861.89245 -859.99252 -859.89862
SM> 0.243E-01 926.91
SM> 47 0.09449 347.7 -861.89379 -859.99312 -859.89862
SM> 0.253E-01 945.46
SM> 48 0.09516 348.7 -861.89494 -859.99378 -859.89862
SM> 0.264E-01 952.41
SM> 49 0.09586 349.5 -861.89587 -859.99448 -859.89862
SM> 0.274E-01 969.87
SM> 50 0.09653 350.0 -861.89654 -859.99515 -859.89862
SM> 0.285E-01 944.25
SM> 51 0.09716 350.2 -861.89691 -859.99578 -859.89862
SM> 0.296E-01 956.94
SM> 52 0.09771 350.2 -861.89697 -859.99632 -859.89861
SM> 0.307E-01 950.04
SM> 53 0.09815 349.9 -861.89670 -859.99676 -859.89861
SM> 0.318E-01 952.96
SM> 54 0.09847 349.5 -861.89611 -859.99708 -859.89861
SM> 0.330E-01 970.18
SM> 55 0.09867 348.8 -861.89518 -859.99727 -859.89860
SM> 0.341E-01 928.44
SM> 56 0.09873 347.9 -861.89393 -859.99733 -859.89860
SM> 0.353E-01 940.75
SM> 57 0.09866 346.8 -861.89235 -859.99726 -859.89860
SM> 0.365E-01 950.19
SM> 58 0.09846 345.5 -861.89042 -859.99705 -859.89859
SM> 0.377E-01 981.22
SM> 59 0.09813 344.0 -861.88816 -859.99672 -859.89859
SM> 0.390E-01 955.57
SM> 60 0.09768 342.3 -861.88555 -859.99627 -859.89859
SM> 0.402E-01 956.94
SM> 61 0.09713 340.2 -861.88259 -859.99571 -859.89859
SM> 0.415E-01 943.63
SM> 62 0.09648 338.0 -861.87928 -859.99506 -859.89858
SM> 0.428E-01 945.27
SM> 63 0.09574 335.5 -861.87563 -859.99432 -859.89858
SM> 0.440E-01 977.58
SM> 64 0.09495 332.7 -861.87166 -859.99353 -859.89857
SM> 0.453E-01 931.39
SM> 65 0.09413 329.6 -861.86739 -859.99270 -859.89857
SM> 0.466E-01 972.12
SM> 66 0.09331 326.3 -861.86286 -859.99187 -859.89856
SM> 0.479E-01 948.16
SM> 67 0.09249 322.8 -861.85810 -859.99105 -859.89856
SM> 0.493E-01 938.37
SM> 68 0.09170 319.0 -861.85316 -859.99026 -859.89855
SM> 0.506E-01 938.60
SM>
SM> Thanks and Regards
SM> Samir
SM>
SM> _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
SM>
SM> Samir H. Mushrif
SM> Department of Chemical Engineering
SM> McGill University
SM> 3610 University Street
SM> Montreal, Quebec H3A2B2
SM> Canada
SM> Ph: (Lab)514-398-5170
SM> (Off)514-398-4169
SM>
--
=======================================================================
Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu
Center for Molecular Modeling -- University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425
=======================================================================
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