[Pw_forum] Error while running metadynamics.
carlo sbraccia
sbraccia at sissa.it
Tue Aug 8 22:38:38 CEST 2006
What you posted is not enough to understand what is wrong in your
calculation: you should send (to the forum or to me directly) the entire
input&output files.
From the Doc/INPUT_PW file:
delta_t REAL ( default = 1.D0 )
delta_t = 1 : every 'nraise' step the actual
temperature is rescaled to
tempw
delta_t /= 1 && delta_T > 0 : at each step the temperature is
multiplied by delta_t; this is
done rescaling all the
velocities.
delta_t < 0 : every 'nraise' steps
temperature
is reduced by -delta_T
Unless you want to change dynamically the temperature (not to be done in
a meta-dynamics run) you shouldn't modify the default value of this
keyword. Also, to run a finite temperature meta-dynamics simulation I
suggest you to set nraise=1.
I add few more comments about meta-dynamics in Quantum-ESPRESSO:
1) The study of a 6-dimensional free-energy surface (FES) is an
EXTREMELY expensive task (in general the computational cost of exploring
an N-dim landscape grows exponentially with N). Maybe that, by using
good collective variables (such as coordination numbers) instead of
simple distances, you can reduce the dimensionality of the FES. In any
case you should consider reducing the number of collective variables.
2) So far meta-dynamics has been used at T=0 only. Finite temperature
simulations are possible, but not yet tested. Moreover, neither the
mean-force corrections nor the dynamical corrections that arise at
finite temperature are implemented (Ciccotti et al.; ChemPhysChem, 6,
1809, 2005). This makes the finite-temperature meta-dynamics which is
implemented in Quantum-ESPRESSO a method only suited for qualitative
studies of the FES.
3) PWscf still lacks a good thermostat like a Nose-Hoover chain. A good
alternative can be the over-damped Langevin dynamics (see keyword
ion_temperature in Doc/INPUT_PW) which, however, still requires some
tuning. The Car-Parrinello code (cp.x) represents an excellent
alternative for finite-temperature simulations.
Regards,
carlo
K.Hari Krishna Reddy wrote:
> Hi
> I'm doing metadynamics on dimethyl-ether(as a test case) using the pwscf
> code(-3.1.1 version). The following are some details from the input file
>
> COLLECTIVE_VARS
> 6
> "distance" 1 2
> "distance" 2 3
> "distance" 3 1
> "distance" 1 5
> "distance" 1 4
> "distance" 1 6
> .....................
>
> ATOMIC_POSITIONS { angstrom }
> C -1.171165000 -0.196607000 0.000000000
> O 0.000000000 0.587847000 0.000000000
> C 1.174595000 -0.195947000 0.000000000
> H -1.242668000 -0.832333000 0.897697000
> H -1.242668000 -0.832333000 -0.897697000
> H -2.020165000 0.493833000 0.000000000
> H 1.231895000 -0.836253000 -0.896096000
> H 1.231895000 -0.836253000 0.896096000
> H 2.021127000 0.495894000 0.000000000
>
> While running the calculation is stopped showing the following error message
>
> " from check_constraint : error # 1
> on some constraint g = 0 is not satisfied"
>
> am a beginner in running dynamics..could anybody help me regarding this
> case. And I also want some explanation regarding the keyword "delta_t" in
> the name list &IONS.
> Thank You
>
>
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