[CPMD-list] Energy components in PIMD

[Łukasz Walewski]

Dear Axel,

Dnia 2008-05-27, wto o godzinie 10:24 -0400, Axel Kohlmeyer pisze:
> On Tue, 27 May 2008, ukasz Walewski wrote:
> 
> LW> Turning back to CP dynamics: my best result (VDB, emass=100 a.u., dt=2
> LW> a.u.) has a drift of 5.5e-5 Ha/ps in fictitious kinetic energy of the
> LW> electrons. This means that during 10 ps run the electronic subsystem
> LW> would gain 0.34 kcal/mol. Can it be assumed acceptable ? What do you
> LW> think of quenching the electrons every 10 ps in the case of longer
> LW> runs ?
> 
> the typical error for DFT calculations can be easily in the 1-2 kcal/mol
> regime, so that seems tolerable although not perfect.
> i'd rather use a thermostat on the electrons (and a small
> overexcitation of the electrons may help to lower artifacts 
> when actual reactions happen, so i'd rather go for the EKINC
> value at the end of the test run than at the beginning as
> target temperature for the electron thermostat.).

Applying a thermostat on the electrons gave the stable fictitious
dynamics, however the conserved energy took over the drift... (see
attached graphs and the input file). Rate of the drift is ~1e-6 Ha/ps,
i.e. smaller by the factor of 10 than the drift in EKINC without a
termostat. My feeling is that it is better to have the total energy
conserved and live with the drift in EKINC. What do you think ?

I turned the restraints on. Following the route you outlined in the
previous e-mail I came upon the kval = 0.000001 [unknown units] which
gives the force of 1.8e-6 [a.u.] in the 1 A distance from the
equilibrium position. The forces usually seen during MD run are of the
order of 1e-3 - 1e-4 while in-plane forces are 1e-5. Isn't it possible
that the drift in EHAM comes from the restraints ?

Regards,
Lukasz
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&CPMD
  MOLECULAR DYNAMICS CP
  RESTART WAVEFUNCTION COORDINATES VELOCITIES NOSEP
  REAL SPACE WFN KEEP
  TIMESTEP
    3.0
  EMASS
    200.0
  TEMPERATURE
    300.0
  NOSE IONS MASSIVE
    300.0  1800.0
  NOSE ELECTRONS
    0.0026 10000.0
  MAXSTEP
    689025
  TRAJECTORY XYZ SAMPLE
    10
  ISOLATED MOLECULE
  CENTER MOLECULE
  STORE
    2000
&END

&SYSTEM
  ANGSTROM
  SYMMETRY
    8
  CELL ABSOLUTE
    13.0 13.0 8.0 0.0 0.0 0.0
  CUTOFF
    35.0
&END

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

&ATOMS
*N_VDB_BLYP.psp FORMATTED
   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_VDB_BLYP.psp FORMATTED
   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_VDB_BLYP.psp FORMATTED
   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
  CONSTRAINTS
    RESPOS 21  0.938025941    3.126976301   -0.723992691  0.0 0.000001
    RESPOS 12 -1.493879250   -5.979008506   -0.097391643  0.0 0.000001
    RESPOS 16 -4.705487062   -1.871875389   -4.515076299  0.0 0.000001
  END CONSTRAINTS
&END