high binding energy

[Sandeep Kumar Reddy]

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

[Sandeep Kumar Reddy]

Hi,

    Towards solving this, I have done binding energy calculations for molecular systems (where they interact through hydrogen bonds) and this value matches with MP2 results. 

It looks like the problem comes in for ionic systems. Did i missed any keyword in my input file ?

Hope this helps somebody to comment on my input file ...

Thanks & Regards,

Sandeep

[Matt W]

Hi Sandeep,

there is nothing very obviously wrong with your input.

Maybe the basis set is not good enough for the anion? You could see whether extra diffuse functions make a big difference...

Matt

[Sandeep Kumar Reddy]

Dear Matt,

                For Br,  DZVP is the large basis set available in cp2k. From last two days, i am continuously running tests on different ion pairs. All calculations show considerable difference compared to MP2 results. 

I will repeat the calculations with extra diffuse functions wherever possible.

(when i did the calculations on different ion-pairs, i got huge differences in some cases also ( -40 kcal/mol difference)

Regards,

Sandeep

--
You received this message because you are subscribed to the Google Groups "cp2k" group.
To view this discussion on the web visit https://groups.google.com/d/msg/cp2k/-/vRFc7PuuJGoJ.
To post to this group, send email to cp...@googlegroups.com.
To unsubscribe from this group, send email to cp2k+uns...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/cp2k?hl=en.

[hut...@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...@pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
---------------------------------------------------------------

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

--
You received this message because you are subscribed to the Google Groups "cp2k" group.

To post to this group, send email to cp...@googlegroups.com.
To unsubscribe from this group, send email to cp2k+uns...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/cp2k?hl=en.

[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]

[Sandeep Kumar Reddy]

Hi,

    I used same functional (BLYP + D) and same Poisson solver, but different PP (Troullier-Martins). I will check with Goedecker PP.

Regards,

Sandeep

1