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Methane: Isotropic model

Summary:

1. ISA charge model for electrostatics. No damping.
2. L1, isotropic undamped polarization model scaled by prefactor to fit better for low interaction energies in the water-methane dimer, see water-methane model*.

3. $C_{6}$, isotropic damped dispersion model.

4. Isotropic exchange-repulsion terms only.

Units: Atomic Units

Citations

• A. J. Misquitta & A. J. Stone, //Ab initio atom–atom potentials using CamCASP: Theory//

Geometry and charges

Source: BS-ISA, A+DF $\zeta=0.1$ aug-cc-pVTZ main basis with aQZ/set2 aux basis. PBE0/AC. CamCASP 5.8.

CH4-ISA.mom

<code | CH4-ISA.mom>

! Based on DF-type : ISA

   C     0.00000000     0.00000000     0.00000000     Type    C      Rank   0
      -0.413530

  H1     0.00000000     2.07703578     0.00000000     Type    H      Rank   0
       0.103598

  H2     1.69589261    -0.69234525     0.97912406     Type    H      Rank   0
       0.103383

  H3    -1.69589261    -0.69234525     0.97912406     Type    H      Rank   0
       0.103383

  H4     0.00000000    -0.69234525    -1.95824810     Type    H      Rank   0
       0.103166

Polarizability

Source: Averaged terms taken from WSM L3,aniso; then multiplied by 1.08735 to better fit low-energy water-methane dimers, see *. Main basis: d-aug-cc-pVTZ; Aux-basis: aug-cc-pVQZ. PBE0/AC with ALDA+CHF kernel. CamCASP 5.8.

CH4-averaged-scaled.pol

<code | CH4-averaged-scaled.pol>
# Static polarizabilities

C C
  0.000  0.0000000      0.0000000      0.0000000
  0.000  6.31667820135      0.0000000      0.0000000
  0.000  0.0000000      6.31667820135      0.0000000
  0.000  0.0000000      0.0000000      6.31667820135

H1 H1
  0.000  0.0000000      0.0000000      0.0000000
  0.000  3.19768616524      0.0000000      0.0000000
  0.000  0.0000000      3.19768616524      0.0000000
  0.000  0.0000000      0.0000000      3.19768616524

H2 H2
  0.000  0.0000000      0.0000000      0.0000000
  0.000  3.19768616524      0.0000000      0.0000000
  0.000  0.0000000      3.19768616524      0.0000000
  0.000  0.0000000      0.0000000      3.19768616524

H3 H3
  0.000  0.0000000      0.0000000      0.0000000
  0.000  3.19768616524      0.0000000      0.0000000
  0.000  0.0000000      3.19768616524      0.0000000
  0.000  0.0000000      0.0000000      3.19768616524

H4 H4
  0.000  0.0000000      0.0000000      0.0000000
  0.000  3.19768616524      0.0000000      0.0000000
  0.000  0.0000000      3.19768616524      0.0000000
  0.000  0.0000000      0.0000000      3.19768616524

Potential & Damping

Coefficients fitted using Orient. Tang-Toennies damping. Single dispersion damping coefficient, no induction damping.

CH4-iso-scaled.pot

<code| CH4-iso-scaled.pot>
C  C           rho       alpha

  Induction DAMPING OFF
  Dispersion damping Factor 1.93
C  C           rho       alpha          C6
   00 00 0   6.227951    2.128586        22.07923
END
C  H           rho       alpha          C6
   00 00 0   4.681533    1.828324        10.09522
END
H  H           rho       alpha          C6
   00 00 0   4.371667    1.535312         4.87260
END

Sample Orient command file

You will need the above files present in the directory as they are included into this Orient file.

Orient version: 4.7/4.8

CH4_2-iso-scaled.ornt

<code | CH4_2-iso-scaled.ornt>

UNITS BOHR

Parameters
      Sites     100 polarizable     100
      S-functions 50000
      Alphas 50000
      Parameter-sets 50000
      Pairs 100000
      Molecules 10
End

Types
       C        Z     6
       H        Z     1
End

Variables
  Rx   10.0 B
  Ry    0.0 B
  Rz    0.0 B
  alpha 0.0 D
  Nx    0.0
  Ny    0.0
  Nz    1.0
  Index  0
End

Molecule  CH4_A at  0 0 0 rotated by 0  about 0 0 1
  #include CH4-ISA.mom
End
Polarizabilities for CH4_A
    Read rank 1
      #include CH4-averaged-scaled.pol
    End
    Limit rank 1 for C H1 H2 H3 H4
End


Molecule  CH4_B at  Rx Ry Rz rotated by alpha  about Nx Ny Nz
  #include CH4-ISA.mom
End
Polarizabilities for CH4_B
    Read rank 1
      #include CH4-averaged-scaled.pol
    End
    Limit rank 1 for C H1 H2 H3 H4
End

Pairs
   #include ./CH4-iso-scaled.pot
End

Units Bohr kJ/mol

Switch Induce On Iterate On
Options
  Induction Iterations 100  Convergence 1e-12
End

Units Bohr kJ/mol


Comment "Energy calculation"
Energy Table Format e15.7 Print es er ind disp total
  Variables
  Index   Rx   Ry   Rz   alpha  Nx  Ny  Nz
    2       0.00   -4.20   0.00    180    1.000   0.000   0.000
    3       0.00   -4.90   0.00    180    1.000   0.000   0.000
    4       0.00   -5.60   0.00    180    1.000   0.000   0.000
    5       0.00   -6.30   0.00    180    1.000   0.000   0.000
    6       0.00   -6.65   0.00    180    1.000   0.000   0.000
    7       0.00   -7.00   0.00    180    1.000   0.000   0.000
    8       0.00   -7.35   0.00    180    1.000   0.000   0.000
    9       0.00   -7.70   0.00    180    1.000   0.000   0.000
   10       0.00   -8.40   0.00    180    1.000   0.000   0.000
   11       0.00   -9.10   0.00    180    1.000   0.000   0.000
   12       0.00   -9.80   0.00    180    1.000   0.000   0.000
End

Finish

Output should end with

end of output

<code | end of output>
         Rx         Ry         Rz      alpha         Nx         Ny         Nz      Index      es         er         ind        disp       total