BOMD - Total energy increasing

[Sandeep Kumar Reddy]

Dear all,
              I am doing an BOMD run of carboxylic acid in water. After 6ps, i plotted conserved quantity as a function of step no.  which shows total energy is increasing.  Can anybody help
why it is increasing ?

Input file :

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME BASIS_MOLOPT
    POTENTIAL_FILE_NAME POTENTIAL
    CHARGE = 0 
    &MGRID
      CUTOFF 280
      NGRIDS 5
      REL_CUTOFF 40
    &END MGRID
     &QS
       METHOD GPW
       EPS_DEFAULT 1.0E-10
     &END QS
     &SCF
       SCF_GUESS ATOMIC
       EPS_SCF 1.0E-6
       MAX_SCF 150
#       MIXING 0.3
       &OUTER_SCF
          EPS_SCF 1.0E-6
          MAX_SCF 50
       &END
    &OT
          MINIMIZER CG
          PRECONDITIONER FULL_ALL
          ENERGY_GAP 0.001
          STEPSIZE 0.05
       &END
 
    &END SCF
    &XC
     &XC_FUNCTIONAL BLYP
      &END XC_FUNCTIONAL
      &vdW_POTENTIAL
         DISPERSION_FUNCTIONAL PAIR_POTENTIAL
         &PAIR_POTENTIAL
            TYPE DFTD2
            REFERENCE_FUNCTIONAL BLYP
         &END PAIR_POTENTIAL
      &END vdW_POTENTIAL
 
   &END XC
  &END DFT

  &SUBSYS
    &CELL
      ABC 12.16174 12.16174 12.16174
    &END CELL

    &COORD
     @INCLUDE coor.xyz
    &END COORD

     &KIND O
      BASIS_SET TZV2P-MOLOPT-GTH-q6
      POTENTIAL GTH-BLYP-q6
    &END KIND
   
    &KIND C
      BASIS_SET TZV2P-MOLOPT-GTH-q4
      POTENTIAL GTH-BLYP-q4
    &END KIND

    &KIND H
      BASIS_SET TZV2P-MOLOPT-GTH-q1
      POTENTIAL GTH-BLYP-q1
      MASS 1.00794
    &END KIND

  &END SUBSYS
&END FORCE_EVAL

&GLOBAL
  PROJECT OUT-URACIL-MD
  RUN_TYPE MD
  PRINT_LEVEL MEDIUM
&END GLOBAL

&MOTION
  &MD
    ENSEMBLE NVT
    STEPS 100000
    TIMESTEP 0.5
    &THERMOSTAT
      &NOSE
        LENGTH 3
        YOSHIDA 3
        TIMECON 100.0
        MTS 2
      &END NOSE
    &END THERMOSTAT
  TEMPERATURE 298.15
  &END MD
&END MOTION


----


Thanks & Regards,
Sandeep kumar Reddy
Ph. D. student

[Axel]

On Friday, July 1, 2011 4:42:40 AM UTC-4, sandeep wrote:

Dear all,
              I am doing an BOMD run of carboxylic acid in water. After 6ps, i plotted conserved quantity as a function of step no.  which shows total energy is increasing.  Can anybody help
why it is increasing ?

half a femtosecond is a pretty aggressive timestep

for a system with non-deuterated hydrogens.

it is a fundamental property of MD simulations

that they don't conserve energy, if you time step 

is too large.

axel.

[hut...@pci.uzh.ch]

Hi

Looking at your energy plot I would guess that the problem is
related to the numerics of the BLYP functional. You can either
increase the energy cutoff from 280 Ry to a considerable higher
value or use a smoothing procedure of the density.
XC_SMOOTH_RHO NN50
would be my choice.

regards

Juerg

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

-----cp...@googlegroups.com schrieb: -----
An: cp...@googlegroups.com
Von: Sandeep Kumar Reddy
Gesendet von: cp...@googlegroups.com
Datum: 07/01/2011 10:42AM
Betreff: [CP2K:3347] BOMD - Total energy increasing

  &END SUBSYS
&END FORCE_EVAL

----

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[Anhang 'Untitled.png' entfernt von Jürg Hutter/at/UZH]

[sandeep]

Thank you, Axel and Juerg . I will try these options and check the
energy conservation.

Regards,
Sandeep

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