[CPMD-list] Energy conservation etc.

[Juerg Hutter]

Hi

One possibility for the energy drift might be the thermostats.
You can try to increase the order of the integrator using
the Nose thermostat options, e.g.

  NOSE PARAMETER
   4 4 4 6 3 25

Have a look in the manual for the meaning of the numbers.

A side note. If you have enough memory available
you can speed up your calculation using

  REAL SPACE WFN KEEP

regards

Juerg Hutter

----------------------------------------------------------
Juerg Hutter                   Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich           E-mail: hutter at pci.unizh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------


On Tue, 1 Nov 2005 padma at uiuc.edu wrote:

> Dear cpmd users,
>
>   I am facing poor energy conservation in CPMD runs of a
> CO2+ water system (one CO2 molecule in 46 H2O) with PBC.
> (The input file used for the MD is given below.)
> The starting configuration was force-field-equilibrated
> structure of the system which is then wavefunction optimized
> to 10.0d-6.
>
> The conservation (slope) of EHAM over a 5 ps run was
> about 10d-4/ps (which, I believe, is atleast one order
> poorer than acceptable value). The kinetic energy of electrons
> and ions looked pretty good with fluctuations about their
> set-values.
>
> Further, hoping that some adjustments in the input parameters
> would improve the situation, a shoter run of about 0.2 ps
> is made (starting from the RESTART file at the end of
> the 5ps run) with the following options:
>
> RESTART LATEST WAVEFUNCTION COORDINATES VELOCITIES NOSEP
>
> QUENCH BO
>
> NOSE IONS
>     300.0  3200.0
> nose electrons
>     0.02  10000.0
>
> (no MASSIVE thermostating for ions and no thermostating
> at all for the electrons)
>
> also in &DFT section the GC-CUTOFF increased
>
>   GC-CUTOFF
>     1.0e-5
>
> But KSH was found greater then EHAM  during the whole run!!
> And the NOSE ENERGY IONS  listed in the AVERAGED QUATITIES at
> the end of the run was negative (~ -0.9 ).
>
> I would be very greatful to know what's going wrong
> and how can I improve the conservation.
>
> best regards,
> Padma
>
>
> &CPMD
>   MOLECULAR DYNAMICS CP
>   optimizE WAVEFUNCTION
>   RESTART LATEST WAVEFUNCTION COORDINATES VELOCITIES NOSEP NOSEE
>   CONVERGENCE
>     1.0e-6  1.0e-6
>   SPLINE POINTS
>     1001
>   TEMPERATURE
>     300.0
>   NOSE IONS MASSIVE
>     300.0  2500.0
>   NOSE ELECTRONS
>     0.02  10000.0
>   MAXSTEP
>     4000
>   TRAJECTORY SAMPLE
>     20
>   TIMESTEP
>     4.0
>   EMASS
>     600.0
> &END
>
> &DFT
>   NEWCODE
>   EXCHANGE CORRELATION TABLE NO
>   FUNCTIONAL BLYP
>   GC-CUTOFF
>     5.0e-6
> &END
>
> &SYSTEM
>   ANGSTROM
>   SYMMETRY
>     1
>   CHARGE
>     0.0
>   CELL
> 11.3 1.0 1.0 0.0 0.0 0.0
>   CUTOFF
>     25.0
> &END
>
>
> &ATOMS
>
> *C_VDB_BLYP.psp NEWF FORMATTED
> LMAX=P
>  1
>
> [COORDINATES ]
>
> *O_VDB_BLYP.psp NEWF FORMATTED
>    LMAX=P
>    48
>
> [ COORDINATES ]
>
> *H_VDB_BLYP.psp NEWF FORMATTED
>    LMAX=S
>    92
>
> [ COORDINATES ]
>
> &END
> _______________________________________________
> CPMD-list mailing list
> CPMD-list at cpmd.org
> http://cpmd.org/mailman/listinfo/cpmd-list
>