[CPMD-list] Energy components in PIMD

[Łukasz Walewski]

Dnia 2008-05-12, pon o godzinie 10:10 -0400, Axel Kohlmeyer pisze:
> On Mon, 12 May 2008, ukasz Walewski wrote:
> 
> LW> Dnia 2008-05-09, piÿÿ o godzinie 10:34 -0400, Axel Kohlmeyer pisze:
> LW> > lukasz,
> LW> > 
> LW> > here is the NC-input that was working well for me.
> LW> 
> LW> Dear Axel,
> LW> 
> LW> I repeated the simulation using your input
> LW> (http://bioexploratorium.pl/ljw/cpmd/nvt/axel/2mdnvt.inp) and I did not
> LW> get the adiabatic behavior - the EKINC drifts from around 0.004 Ha
> LW> initially to 0.008 Ha after 7ps
> 
> since the machine i have available for these kinds of tests, 
> i cannot run that long. please see the first attached graph. 
> it does show a little slant now.

Going down to 200 a.u. with e-mass seems to stabilize the drift in EKINC
more or less (with the timestep of 3 a.u) - see attached graph. Do you
think it's reasonable ? Would it be sane to go even to 150 a.u. and
possibly reducing the time step to 2 a.u. (having the future PIMD
simulations in mind) ? 

> BTW: based on its "spectrum" i have changed coupling frequency
> for the N-H chains to 2500 cm-1, if you look at the second 
> attached graph this seems a much more reasonable choice as it

What do you call "spectrum" in this case ? - with FFT(EKINC) I get
something different...

> when you turn on path-integrals, you _will_ have to reduce the time step, 
> anyways (unless you run BO-dynamics).

I will try to reduce the time step to 3 a.u. and the e-mass to 200 a.u.
but increase ecutoff to 35 Ry (or even to more) in the case of VDB
pseudopotentials - hopefully this will allow for longer PIMD run...

There is one more issue regarding the COM. The second attached plot
shows the conserved energy, that exhibits jumps every 2500 steps - that
is every time I SUBTRACT COMVEL ROTVEL. The jumps occur on the fifth
decimal place in Ha. Would you accept such behavior ? (I know one should
not rescale velocities when using NH thermostat but the manual is
equivocal on what is already a bad thing.)

Regards,
Lukasz

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&CPMD
  MOLECULAR DYNAMICS CP
  RESTART WAVEFUNCTION COORDINATES LATEST
  REAL SPACE WFN KEEP
  TIMESTEP
    3.0
  EMASS
    200.0
  TEMPERATURE
    300.0
  NOSE IONS MASSIVE
    300.0  1800.0
  MAXSTEP
    137805
  SUBTRACT COMVEL ROTVEL
    2500
  TRAJECTORY XYZ SAMPLE
    -10
  ISOLATED MOLECULE
  CENTER MOLECULE
  STORE
    1000
&END

&SYSTEM
  ANGSTROM
  SYMMETRY
    8
  CELL ABSOLUTE
    13.0 13.0 8.0 0.0 0.0 0.0
  CUTOFF
    70.0
&END

&DFT
  FUNCTIONAL BLYP
  GC-CUTOFF
    5.D-6
&END

&ATOMS
*N_MT_BLYP.psp KLEINMAN-BYLANDER
   LMAX=P
   4
       1.480434744000      -1.261526338000       0.012486679000
      -1.428836888000      -1.263268937000       0.020030520000
      -1.482423266000       1.260607946000       0.012029901000
       1.430161665000       1.261259358000       0.004480994000
*C_MT_BLYP_1.psp KLEINMAN-BYLANDER
   LMAX=P
   20
       2.764321879000       1.617573818000      -0.000125061000
       3.855614684000       0.719804456000      -0.000057419000
       3.883340408000      -0.678014026000       0.004378686000
       2.816852951000      -1.603192445000       0.010125751000
       2.919542448000      -3.046779447000       0.014515219000
       1.637225743000      -3.547145051000       0.019451505000
       0.739381956000      -2.412298909000       0.018118048000
      -0.677939805000      -2.411241253000       0.021787063000
      -1.565841060000      -3.552172948000       0.027767194000
      -2.851571375000      -3.063067365000       0.029521295000
      -2.763080194000      -1.618905630000       0.024634604000
      -3.853925457000      -0.720052370000       0.024562307000
      -3.883570717000       0.678208069000       0.020129751000
      -2.818027537000       1.604764172000       0.014380689000
      -2.917826697000       3.049092800000       0.009981340000
      -1.634343765000       3.546387751000       0.005051935000
      -0.738698022000       2.409860388000       0.006396510000
       0.678687181000       2.408624576000       0.002727905000
       1.566148163000       3.550017372000      -0.003252572000
       2.852089024000       3.061544408000      -0.005009259000
*H_MT_BLYP.psp KLEINMAN-BYLANDER
   LMAX=S
   14
       4.829896620000       1.209449328000      -0.004160981000
       4.874865030000      -1.131837359000       0.003273118000
       3.847285348000      -3.609138791000       0.013924943000
       1.339951403000      -4.589537686000       0.023583475000
      -1.257219301000      -4.591087509000       0.030318008000
      -3.775889801000      -3.630740840000       0.033747037000
      -4.828126595000      -1.209793447000       0.028665970000
      -4.875902354000       1.130204086000       0.021243303000
      -3.843471723000       3.614955577000       0.010554882000
      -1.334243713000       4.588096584000       0.000914849000
       1.257025926000       4.588704910000      -0.005801358000
       3.776400021000       3.629099090000      -0.009234599000
       1.216317908000      -0.004972921000       0.009118666000
      -1.218997172000       0.003787130000       0.015400566000
&END