CH₄+HgCl₂⇔CH₃HgCl+HCl: a TS search

Sample directory: adf/RelTS_CH4_HgCl2/

A Transition State calculation, including scalar relativistic terms in the Hamiltonian.

First the relativistic core potentials are generated.

$ADFBIN/dirac -n1 < $ADFRESOURCES/Dirac/Hg.4d
$ADFBIN/dirac -n1 < $ADFRESOURCES/Dirac/Cl.2p
$ADFBIN/dirac -n1 < $ADFRESOURCES/Dirac/C.1s
$ADFBIN/dirac -n1 < $ADFRESOURCES/Dirac/H

mv TAPE12 t12.rel

Then the (relativistic) Create runs.

$ADFBIN/adf << eor
create Hg $ADFRESOURCES/TZP/Hg.4d
relativistic
corepotentials t12.rel &
Hg 1
end
end input
eor

mv TAPE21 t21.Hg


$ADFBIN/adf << eor
create Cl $ADFRESOURCES/TZP/Cl.2p
relativistic
corepotentials t12.rel &
Cl 2
end
end input
eor

mv TAPE21 t21.Cl

$ADFBIN/adf << eor
create C $ADFRESOURCES/TZP/C.1s
relativistic
corepotentials t12.rel &
C  3
end
end input
eor

mv TAPE21 t21.C


$ADFBIN/adf << eor
create H $ADFRESOURCES/TZP/H
relativistic
corepotentials t12.rel &
H  4
end
end input
eor

mv TAPE21 t21.H

In the first Create run (Hg) the CorePotentials key could have been used in its simple form, but in the second (and third and fourth, omitted here) the block form is required to identify the appropriate section on TAPE12 for the atom at hand. In the first case we could have relied on the default: the first section on TAPE12 for the first (in this case: only) atom type.

Note that even for H, which obviously has no frozen core at all, we specify the TAPE12 corepotentials file and indicate the appropriate section for H. The reason is that TAPE12 contains not only the (frozen) core, but also the total atomic (relativistic) potential.

Finally the TS run.

$ADFBIN/adf << eor
TITLE  Transition State: CH4 + HgCl2  <===>  CH3HgCl + HCl

noprint sfo,frag
print atdist

GEOMETRY
  TransitionState
END

relativistic
corepotentials  t12.rel &
C   3
Hg  1
Cl  2
H   4
end

XC
lda  VWN Stoll
END

DEFINE
  rHg = 2.30
  rX1 = 2.35
  rX2 = 2.90
  rH1 = 1.10
  rH2 = 1.10
  rH3 = 1.40

  aX1 = 160
  aX2 = 70
  aH1 = 100
  aH2 = 140
  aH3 = 65

  dH  = 60
END

ATOMS     Z-Matrix
  1.  C     0  0  0   0.        0.        0.
  2.  Hg    1  0  0   rHg       0.        0.
  3.  Cl    2  1  0   rX1      aX1        0.
  4.  H     1  2  3   rH1      aH1       dH
  5.  H     1  2  3   rH1      aH1      -dH
  6.  H     1  2  3   rH2      aH2       180.
  7.  H     1  2  3   rH3      aH3       180.
  8.  Cl    2  1  3   rX2      aX2       180.
END

FRAGMENTS  
 Hg   t21.Hg
 C    t21.C
 H    t21.H
 Cl   t21.Cl
END

endinput
eor

For the density-functional the Local Density approximation is used (no GGA corrections), with a correlation correction term due to Stoll (see the User's Guide).

At each geometry cycle the interatomic distance matrix is printed (print atdist).

The initial geometry is a reasonable but not very accuracte estimate of the Transition State. The program needs quite a few cycles to converge, which is rather typical for ts searches: they are a lot more tricky and fail more often than a simple minimization.