[CPMD-list] help regarding PIMD

[Tuhina Kelkar]

Hello Everyone!

I am a new user of CPMD and am keen on using the PIMD option for some simple
metal hydrides. I began by equilibrating my system without thermostats. In
the next step I ran a short MD with NOSE IONS and obtained an average value
for EKINC. I then ran another short MD where I added the NOSE ELECTRONS. I
used the restart generated here to run (1) a CPMD simulation and (2) a PIMD
simulation with classical option. Comparing the results of these
simulations, as expected the values of EKINC, TEMPP, EKS, ECLASSIC and EHAM
at each time step were calculated to be the same. But the average quantities
of the above energies printed at the end of the PIMD+classical case were
way different from those obtained from the CPMD simulations.

I am unable to understand that while the energies at each step match their
averages do not. Could someone help me in this regard? Why is this
happening? Are these averages calculated differently? I am copying below the
input files (minus the ATOMS section) and average quantities obtained from
the 2 simulations for you to see.

With regards,
Tuhina

(1) &INFO
mgh2
stage 4 of CPMD
&END
&CPMD
MOLECULAR DYNAMICS CP
RESTART COORDINATES WAVEFUNCTION LATEST
RESTART NOSEP NOSEE
RESTART VELOCITIES
TIMESTEP
5.0
NOSE IONS
300 2000.0
NOSE ELECTRONS
0.006 9000
TRAJECTORY SAMPLE XYZ
5
PRINT
20
MAXSTEP
500
EMASS
400
&END
&DFT
FUNCTIONAL GGA (=PW91)
&END
&SYSTEM
SYMMETRY
6
SCALE
CELL ABSOLUTE DEGREE
16.9730 16.9730 11.3209 90.0 90.0 90.0
CUTOFF
35
&END


 ****************************************************************
 *                      AVERAGED QUANTITIES                     *
 ****************************************************************
                              MEAN VALUE       +/-  RMS DEVIATION
                                     <x>     [<x^2>-<x>^2]**(1/2)
 ELECTRON KINETIC ENERGY    0.594767E-02             0.705827E-03
 IONIC TEMPERATURE                288.11                    24.69
 DENSITY FUNCTIONAL ENERGY    -33.122802             0.642653E-02
 CLASSICAL ENERGY             -32.995247             0.692273E-03
 CONSERVED ENERGY             -32.989299             0.200328E-04
 NOSE ENERGY ELECTRONS          0.006899             0.146511E-02
 NOSE ENERGY IONS               0.056337             0.509951E-02
 CONSTRAINTS ENERGY             0.000000              0.00000
 ION DISPLACEMENT           0.219204                 0.859291E-01
 CPU TIME                         0.4549
 ****************************************************************

(2)&INFO
mgh2
pimd under classical test
&END
&CPMD
MOLECULAR DYNAMICS CP
PATH INTEGRAL
RESTART COORDINATES WAVEFUNCTION LATEST
RESTART NOSEP NOSEE
RESTART VELOCITIES ACCUMULATORS
TIMESTEP
5.0
NOSE IONS
300 2000.0
NOSE ELECTRONS
0.006 9000
TRAJECTORY SAMPLE XYZ
5
PRINT
20
MAXSTEP
500
EMASS
400
&END
&PIMD
CLASSICAL TEST
&
&DFT
FUNCTIONAL GGA (=PW91)
&END
&SYSTEM
SYMMETRY
6
SCALE
CELL ABSOLUTE DEGREE
16.9730 16.9730 11.3209 90.0 90.0 90.0
CUTOFF
35
&END

 ****************************************************************
 *                      AVERAGED QUANTITIES                     *
 ****************************************************************
                              MEAN VALUE       +/-  RMS DEVIATION
                                     <x>     [<x^2>-<x>^2]**(1/2)
 ELECTRON KINETIC ENERGY     313.214                  313.214
 IONIC TEMPERATURE                205.79                   131.82
 DENSITY FUNCTIONAL ENERGY    287.379817              286.013
 QUANTUM KINETIC ENERGY(P)      0.047852             0.302409E-01
 QUANTUM KINETIC ENERGY(V)  25492.050728              25492.1
 TOTAL QUANTUM ENERGY(P)      -23.611303              14.9331
 CLASSICAL ENERGY             287.357202              286.001
 CONSERVED ENERGY             -23.563769              14.9031
 ION DISPLACEMENT           0.230188                 0.291464E-01
 CPU TIME                         0.4532

---------------------------------------------------------------------------
Tuhina Kelkar
c/o Dr. Sourav Pal
Physical Chemistry Division,
National Chemical Laboratory,
Pune - 411008
INDIA
-----------------------------------------------------------
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