Lagrangian metadynamics parameters & tuning

[alh chin]

Dear all, 

I want to use Lagrangian MTD to study a reaction (since the barrier appears to be high), I checked the CP2K manuals and the example at exercises:2015_cecam_tutorial:mtd1 [CP2K Open Source Molecular Dynamics ]

I found that I need to specify 4 parameters for Lagrangian MTD, 

(1)TEMPERATURE

(2)TEMP_TOL  

and for each CV, 

(3) LAMBDA

(4) MASS

my questions are 

(1) I understand why TEMPERATURE need to be specified, but why TEMP_TOL (temperature tolerance) has to be specified?

(2) is LAMBDA the force constant for the fictitious particle? what's the unit?

(3) what would be good values for TEMP_TOL and (most importantly) LAMBDA, and, how to tune LAMBDA? 

Thanks,

Alh.

[Marcella Iannuzzi]

Dear Alh.

If not specified, the temperature is set to the system's temperature

The tolerance for the temperature can but must not be specified. 

The units of the force constant are atomic units.

The choice of all these parameters is system dependent.  

Preparatory runs to explore the system's behaviour are strongly recommended to help in choosing the proper settings.

Regards

Marcella

[alh chin]

Dear Marcella, 

Thank you very much for your reply.  I found a few papers that discuss the tuning of the force constants, e.g., Ensing et al., (J. Phys. Chem. B 2005, 109, 6676-6687). From what I understand, the force constant has to be tuned such that the path of the fictitious particle is not that far away from the real CV path. So I need to prepare some data of the fictitious particle (with test runs). I would expect these data to be stored in a file called XXX_COLVAR.metadynLog.

In the example you explained that columns in the metadynLog file are CVs, gradients of the bias potential wrt CVs, gradients of the wall wrt CVs, values of the bias potentials, values of the wall potentials.

I would expect if a Lagrangian MTD is run, the coordinates of fictitious particle would be monitored in the metadynLog.

QUESTION:  what are the columns in the metadynLog file for a Lagrangian MTD

thanks, 

Alh,

------------------

(the example you provided is below, I would guess the final one is temp)

         0.0     2.71770373     1.42316747     0.11550959     2.71061596     1.42089234     0.11424663     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00021431     0.00006879     0.00003819     0.00000000     0.00000000     0.00000000   300.00000000

         0.8     2.72482415     1.42536380     0.11672755     2.71045717     1.41982383     0.11363373    -0.01811640    -0.01003091    -0.00562756     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00021529     0.00006641     0.00003683     0.00008769     0.00000000     0.00000000   300.00000000

         1.6     2.73206759     1.42720809     0.11779474     2.71219970     1.41629628     0.11236277    -0.03156113    -0.02720256    -0.01309435     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00021901     0.00005576     0.00003227     0.00035113     0.00000000     0.00000000   300.00000000

with the input file:

&FREE_ENERGY

    &METADYN

      DO_HILLS 

      NT_HILLS 100

      WW 2.0e-3

      LAGRANGE

      TEMPERATURE 300.

      TEMP_TOL  10.

      &METAVAR

        LAMBDA  2.5

        MASS   30.

        SCALE 0.1

        COLVAR 1

      &END METAVAR

      &METAVAR

        LAMBDA 3.0

        MASS 30.0

        SCALE 0.25

        COLVAR 2

      &END METAVAR

      &METAVAR

        LAMBDA 3.0

        MASS 30.0

        SCALE 0.25

        COLVAR 3

        &WALL

            POSITION 0.0

            TYPE QUARTIC

            &QUARTIC

               DIRECTION WALL_MINUS

               K  100.0

            &END

        &END

      &END METAVAR

      &PRINT

        &COLVAR

           COMMON_ITERATION_LEVELS 3

           &EACH

             MD 1

           &END

        &END

        &HILLS

           COMMON_ITERATION_LEVELS 3

           &EACH

             MD 1

           &END

        &END

      &END

    &END METADYN

  &END

  &PRINT

    &TRAJECTORY

      &EACH

        MD 50

      &END

    &END

    &VELOCITIES OFF

    &END

    &RESTART

      &EACH

         MD 100

      &END

      ADD_LAST NUMERIC

    &END

    &RESTART_HISTORY 

      &EACH

         MD 2000

      &END

    &END

  &END

&END MOTION

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[Marcella Iannuzzi]

For the specific case

time     metavar1        metavar2          metavar3             CV1                   CV2                 CV3                    FH1                    FH2                  FH3                  MTDF1               MTDF2              MTDF3             WF1                     WF2                     WF3                VEL1       VEL2                   VEL3                    HPOT           MTDPOT              WALLPOT        TEMP

0.0     2.71770373     1.42316747     0.11550959     2.71061596     1.42089234     0.11424663     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00000000     0.00021431     0.00006879     0.00003819     0.00000000     0.00000000     0.00000000   300.00000000

where FH is the force contribution on metavar from the harmonic potential, MTDF is the force contribution from the MTD potential, WF is the force contribution from the wall potential

The rest should be selfexplaining.

Regards

Marcella