MM Dispersion: Molecular Mechanics dispersion-corrected functionals

 

Sample directory: adf/MM_Dispersion/

Summary:

• MM dispersion (old implementation)
• Dispersion-corrected GGA-D functionals

MM dispersion (old implementation)

First example shows a geometry optimization of a van der Waals complex of two benzene molecules, connected to each other with a hydrogen molecule. With the MMDISPERSION keyword an extra empirical force (of similar form as in molecular mechanics) is added to the interaction between the three fragments, where one benzen molecule is fragment 1 (FD=1), the other benzene molecule is fragment 2 (FD=2), and the hydrogen molecule is fragment 3 (FD=3).

The atomic parameters are read from the file $ADFRESOURCES/MMDispersion/disp-param. The PBE functional and the TZP basis set are used, which is necessary if one wants to use the TZ parameters for the damping function, which are optimized for this combination of functional and basis set.

$ADFBIN/adf << eor
basis
  type TZP
  core small
End
XC
  GGA PBE 
End
geometry
  converge grad=0.001
  iterations 5
end
Integration  4.5
SCF
  Iterations  60
  Converge  1.0E-06  1.0E-6
End
mmdispersion
  damping sigm
  damp_param tz
  combi s-k
  file_name $ADFRESOURCES/MMDispersion/disp-param
  nodefault
end
noprint sfo
Atoms   cartesians
C.ctr  0.000000000000     3.050000000000     1.391500000000  FD=1
H.h    0.000000000000     3.050000000000     2.471500000000  FD=1
C.ctr  1.205074349366     3.050000000000     0.695750000000  FD=1
H.h    2.140381785453     3.050000000000     1.235750000000  FD=1
C.ctr  1.205074349366     3.050000000000    -0.695750000000  FD=1
H.h    2.140381785453     3.050000000000    -1.235750000000  FD=1
C.ctr -0.000000000000     3.050000000000    -1.391500000000  FD=1
H.h   -0.000000000000     3.050000000000    -2.471500000000  FD=1
C.ctr -1.205074349366     3.050000000000    -0.695750000000  FD=1
H.h   -2.140381785453     3.050000000000    -1.235750000000  FD=1
C.ctr -1.205074349366     3.050000000000     0.695750000000  FD=1
H.h   -2.140381785453     3.050000000000     1.235750000000  FD=1
C.ctr -1.205074349366    -3.050000000000    -0.695750000000  FD=2
H.h   -2.140381785453    -3.050000000000    -1.235750000000  FD=2
C.ctr -0.000000000000    -3.050000000000    -1.391500000000  FD=2
H.h   -0.000000000000    -3.050000000000    -2.471500000000  FD=2
C.ctr  1.205074349366    -3.050000000000    -0.695750000000  FD=2
H.h    2.140381785453    -3.050000000000    -1.235750000000  FD=2
C.ctr  1.205074349366    -3.050000000000     0.695750000000  FD=2
H.h    2.140381785453    -3.050000000000     1.235750000000  FD=2
C.ctr -0.000000000000    -3.050000000000     1.391500000000  FD=2
H.h   -0.000000000000    -3.050000000000     2.471500000000  FD=2
C.ctr -1.205074349366    -3.050000000000     0.695750000000  FD=2
H.h   -2.140381785453    -3.050000000000     1.235750000000  FD=2
H.h    0.0                0.35               0.0             FD=3
H.h    0.0               -0.35               0.0             FD=3
End
End Input

The part of the bond energy that is due to the Grimme dispersion corrected functional is only inter-molecular (atom-atom contributions for which the fragment numbers FD are different).

Dispersion-corrected GGA-D functionals

In the second example a structure with 2 benzene molecules and a hydrogen molecule is optimized with the Grimme dispersion corrected PBE. Needed is the subkey DISPERSION in the key XC. If one starts with atomic fragments the part of the bond energy that is due to the Grimme dispersion corrected functional is both inter-molecular as well as intra-molecular. In this case the subargument FD= in the ATOMS block key word is not used, which was only used in the old MM dispersion calculation.

$ADFBIN/adf << eor
Title Geometry optimization with Grimme dispersion correction for GGA
basis
  type TZP
  core small
End
XC
  GGA PBE 
  DISPERSION
End
geometry
  converge grad=0.001
  Branch OLD
  iterations 50
end
Integration  4.5
Atoms   cartesians
C  0.000000000000     3.050000000000     1.391500000000
H  0.000000000000     3.050000000000     2.471500000000
C  1.205074349366     3.050000000000     0.695750000000
H  2.140381785453     3.050000000000     1.235750000000
C  1.205074349366     3.050000000000    -0.695750000000
H  2.140381785453     3.050000000000    -1.235750000000
C -0.000000000000     3.050000000000    -1.391500000000
H -0.000000000000     3.050000000000    -2.471500000000
C -1.205074349366     3.050000000000    -0.695750000000
H -2.140381785453     3.050000000000    -1.235750000000
C -1.205074349366     3.050000000000     0.695750000000
H -2.140381785453     3.050000000000     1.235750000000
C -1.205074349366    -3.050000000000    -0.695750000000
H -2.140381785453    -3.050000000000    -1.235750000000
C -0.000000000000    -3.050000000000    -1.391500000000
H -0.000000000000    -3.050000000000    -2.471500000000
C  1.205074349366    -3.050000000000    -0.695750000000
H  2.140381785453    -3.050000000000    -1.235750000000
C  1.205074349366    -3.050000000000     0.695750000000
H  2.140381785453    -3.050000000000     1.235750000000
C -0.000000000000    -3.050000000000     1.391500000000
H -0.000000000000    -3.050000000000     2.471500000000
C -1.205074349366    -3.050000000000     0.695750000000
H -2.140381785453    -3.050000000000     1.235750000000
H  0.0                0.35               0.0           
H  0.0               -0.35               0.0           
End
End Input

In the last example first three molecules (2 benzene molecules and a hydrogen molecule) are calculated with the Grimme dispersion corrected PBE. Needed again is the subkey DISPERSION in the key XC. The one for H₂ is given below:

$ADFBIN/adf << eor
Title Grimme dispersion-corrected GGA
basis
  type TZP
  core small
End
XC
  GGA PBE 
  DISPERSION
End
SCF
  Iterations  60
  Converge  1.0E-06  1.0E-6
End
Atoms
H         0.000000    0.000000   -0.377906
H         0.000000    0.000000    0.377906
End
End Input
eor
mv TAPE21 h2.t21

Note that even for such a molecule there is a contribution from the so called Dispersion energy in the bonding energy (although it will be very small in this case).

Next a structure is calculated in which the three calculated molecules in it. If one starts with molecular fragments the part of the bond energy that is due to the Grimme dispersion corrected functional is only inter-molecular.

$ADFBIN/adf << eor
Title Grimme dispersion-corrected GGA
Fragments
  b1 benzene1.t21
  b2 benzene2.t21
  h2 h2.t21
End
XC
  GGA PBE 
  DISPERSION
End
Atoms
C         0.000000    1.398973   -3.054539  f=b1
H         0.000000    2.490908   -3.049828  f=b1
C         1.211546    0.699486   -3.054539  f=b1
H         2.157190    1.245454   -3.049828  f=b1
C         1.211546   -0.699486   -3.054539  f=b1
H         2.157190   -1.245454   -3.049828  f=b1
C         0.000000   -1.398973   -3.054539  f=b1
H         0.000000   -2.490908   -3.049828  f=b1
C        -1.211546   -0.699486   -3.054539  f=b1
H        -2.157190   -1.245454   -3.049828  f=b1
C        -1.211546    0.699486   -3.054539  f=b1
H        -2.157190    1.245454   -3.049828  f=b1
C        -1.211546   -0.699486    3.054539  f=b2
H        -2.157190   -1.245454    3.049828  f=b2
C         0.000000   -1.398973    3.054539  f=b2
H         0.000000   -2.490908    3.049828  f=b2
C         1.211546   -0.699486    3.054539  f=b2
H         2.157190   -1.245454    3.049828  f=b2
C         1.211546    0.699486    3.054539  f=b2
H         2.157190    1.245454    3.049828  f=b2
C         0.000000    1.398973    3.054539  f=b2
H         0.000000    2.490908    3.049828  f=b2
C        -1.211546    0.699486    3.054539  f=b2
H        -2.157190    1.245454    3.049828  f=b2
H         0.000000    0.000000   -0.377906  f=h2
H         0.000000    0.000000    0.377906  f=h2
End
End Input
eor

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