[CP2K:3886] high binding energy

[hut... at pci.uzh.ch]

Hi

Maybe you should really use exactly the same setup (Basis and Functional using GAPW) as
a starting point and then step for step introduce pseudopotentials and
other basis sets and e.g. dispersion corrections.
The comparision with CPMD has been done with the same PP and functionals (BLYP+D2),
and Poisson solver?
If yes, this would point towards a basis set problem.

Juerg 

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

-----cp... at googlegroups.com wrote: -----
To: cp... at googlegroups.com
From: Sandeep Kumar Reddy 
Sent by: cp... at googlegroups.com
Date: 07/02/2012 03:13PM
Subject: [CP2K:3886] high binding energy

Dear all,  
             I want to calculate binding energy and compare with Gaussian's result and then i would like to proceed to bulk simulations.

My system one ion pair (it's an ionic liquid). I did geometry optimizations of cation, anion and ion-pair and calculated the binding energy. This value is equal to  -119 kcal/mol. After adding BSSE corrections, it is reduced to -116 kcal/mol. For comparison, i carried out same calculations at MP2/aug-cc-pVDZ level using Gaussian package and this value is equal to -104 kcal/mol (BSSE corrected). A difference of 10 kcal/mol of such calculation is discouraging.  

(I have used same functional, cell parameters, cutoff, potentials for all three calculations)


I repeated the calculations by changing cutoff (to 480 Ry) and increasing box length (20 \AA). But it gives me same binding energy. Additionally, i have done same calculations in plane wave basis set using CPMD code. It gives 105 kcal/mol, very close to MP2 result.  

I am not able to figure out why it happens.  Could anybody comment on my input files ?


Ion-pair :

&GLOBAL
  PROJECT dimethyl_ammonium_bromide 
  RUN_TYPE GEO_OPT
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME  /panfs/home/Xsreddy/cp2k/tests/QS/BASIS_MOLOPT 
    POTENTIAL_FILE_NAME  /panfs/home/Xsreddy/cp2k/tests/QS/POTENTIAL
    &MGRID
      CUTOFF 280
      NGRIDS 5
    &END MGRID
    &QS
      METHOD       GPW     
      EPS_DEFAULT  1.0E-10 
    &END QS 
    &SCF
      MAX_SCF   50
      EPS_SCF   1.0E-6
      SCF_GUESS ATOMIC
      &OT ON
        MINIMIZER       CG 
        PRECONDITIONER  FULL_ALL
        ENERGY_GAP      0.001
      &END OT
      &OUTER_SCF
        MAX_SCF  100
        EPS_SCF  1.0E-6  
      &END OUTER_SCF 
    &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
     &POISSON
     POISSON_SOLVER WAVELET
     PERIODIC NONE
    &END POISSON
  &END DFT
  &SUBSYS
    &CELL
      ABC 20.0 20.0 20.0 
      PERIODIC NONE
    &END CELL
    &COORD
    H       1.82622900    0.00011700    1.45609900
    H       0.41368700   -0.00011700    0.43855600
    N       1.53927100    0.00002300    0.47861600 
    C       1.97625500   -1.24136700   -0.20041700
    H       3.06445100   -1.28419200   -0.25417500 
    H       1.58040100   -2.09266400    0.34985900 
    H       1.53907000   -1.23367800   -1.19754500  
    C       1.97589400    1.24149000   -0.20039300 
    H       1.54099200    1.23242900   -1.19850300 
    H       1.57755100    2.09264100    0.34831700 
    H       3.06414500    1.28582600   -0.25177600  
    Br     -1.40269500   -0.00003600   -0.01818000 
    &END COORD
    &TOPOLOGY
      &CENTER_COORDINATES
      &END
    &END 
    &KIND H    
      BASIS_SET  DZVP-MOLOPT-GTH
      POTENTIAL  GTH-BLYP-q1
    &END KIND 
    &KIND C
      BASIS_SET  DZVP-MOLOPT-GTH
      POTENTIAL  GTH-BLYP-q4
     &END KIND 
    &KIND N
      BASIS_SET  DZVP-MOLOPT-GTH
      POTENTIAL  GTH-BLYP-q5
    &END KIND 
    &KIND Br
      BASIS_SET  DZVP-MOLOPT-SR-GTH 
      POTENTIAL  GTH-BLYP-q7 
    &END KIND 
  &END SUBSYS
&END FORCE_EVAL
&MOTION
  &GEO_OPT
    MAX_FORCE 0.0001
    MAX_ITER 500 
    OPTIMIZER BFGS
  &END GEO_OPT
&END MOTION 


Other input files are enclosed. 

Thanks.

Regards,
 Sandeep








  
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[attachment "ion-pair.in" removed by Jürg Hutter/at/UZH]
[attachment "cation.in" removed by Jürg Hutter/at/UZH]
[attachment "anion.in" removed by Jürg Hutter/at/UZH]