Example: FDE freeze-and-thaw: HeCO2

Download FDE_HeCO2_freezeandthaw.run

This example demonstrates how a freeze-and-thaw FDE calculation can be performed. As test system, a He-CO2 van der Waals complex is used. It will further be shown how different exchange-correlation potential can be used for different subsystems, and how different basis set expansions can be employed. For details, see C.R. Jacob, T.A. Wesolowski, L. Visscher, J. Chem. Phys. 123 (2005), 174104. It should be stressed that the basis set and integration grid used in this example are too small to obtain good results.

Summary:

  • PW91 everywhere
  • SAOP for He; PW91 for CO2
  • FDE(s) calculation with PW91 everywhere

Important, this kind of FDE geometry optimization only works with the non-default STO pair fitting method. This means that one has to include the key STOFIT in the input for ADF. If one does not use the BASIS key, like in this example, one should also include the key STOFIT in all fragment calculations (also in the create runs).

PW91 everywhere

In the first part, the PW91 functional will be used for both the He and the CO2 subsystems. In this part, the FDE(m) basis set expansion is used, i.e., basis functions of the frozen subsystem are not included in the calculation of the nonfrozen subsystem.

First, the CO2 molecule is prepared. In this calculation, the C2v symmetry of the final complex is used, and the NOSYMFIT option has to be included because this molecule will be rotated as a frozen fragment.

$ADFBIN/adf << eor
Title TEST 1 -- Preparation of frozen CO2
STOFIT

Units
 Length Bohr
end

Atoms
C          0.000000  0.000000  0.000000
O         -2.192000  0.000000  0.000000
O          2.192000  0.000000  0.000000
end

Symmetry C(2V)
NOSYMFIT

Fragments
 C  t21.C
 O  t21.O
End

integration 5.0

xc
 GGA pw91
end

End Input
eor

mv TAPE21 t21.co2.0

Afterwards, the FDE calculation is performed. In this calculation, the He atom is the nonfrozen system, and the previously prepared CO2 molecule is used as frozen fragment. For this frozen fragment the RELAX option is specified, so that the density of this fragment is updated in freeze-and-thaw iteration (a maximum number of three iteration is specified).

$ADFBIN/adf << eor
Title TEST 1 -- Embedding calculation: He + frozen CO2 density -- freeze-and-thaw
STOFIT

Units
 Length Bohr
end

Atoms
 He   0.000000  0.000000  6.019000 f=He
 C    0.000000  0.000000  0.000000 f=co2
 O   -2.192000  0.000000  0.000000 f=co2
 O    2.192000  0.000000  0.000000 f=co2
end

Fragments
 He   t21.He
 co2  t21.co2.0  type=fde
   fdeoptions RELAX
 SubEnd
End

NOSYMFIT

integration 5.0

xc
 GGA pw91
end

FDE
 PW91K
 FULLGRID
 RELAXCYCLES 3
end

End Input
eor

SAOP for He; PW91 for CO2

In this second part, the above example is modified such that PW91 is employed for the CO2 subsystem, while the SAOP potential is used for He. This can be achieved by choosing SAOP in the XC key (this sets the functional that will be used for the nonfrozen subsystem). Additionally, for the frozen fragment the XC option is used to chose the PW91 functional for relaxing this fragment. Furthermore, the PW91 functional is chosen for the nonadditive exchange-correlation functional that is used in the embedding potential with the GGAPOTXFD and GGAPOTCFD options in the FDE key.

$ADFBIN/adf << eor
Title TEST 2 -- Embedding calculation: He + frozen CO2 density -- freeze-and-thaw
STOFIT

Units
 Length Bohr
end

Atoms
 He   0.000000  0.000000  6.019000 f=He
 C    0.000000  0.000000  0.000000 f=co2
 O   -2.192000  0.000000  0.000000 f=co2
 O    2.192000  0.000000  0.000000 f=co2
end

Fragments
 He   t21.He
 co2  t21.co2.0  type=fde
   fdeoptions RELAX
   XC         GGA PW91
 SubEnd
End

NOSYMFIT

integration 5.0

xc
 MODEL SAOP
end

FDE
 PW91K
 FULLGRID
 GGAPOTXFD PW91x
 GGAPOTCFD PW91c
 RELAXCYCLES 3
end

End Input
eor

FDE(s) calculation with PW91 everywhere

In this third part, the PW91 functional is applied for both subsystems again, but in contrast to part 1, now the FDE(s) basis set expansion is used, i.e., the basis functions of the frozen subsystem are included in the calculation of the nonfrozen subsystem. This can be achieved by employing the USEBASIS option. This option can be combined with the RELAX option.

$ADFBIN/adf << eor
Title TEST 3 -- Embedding calculation: He + frozen CO2 density -- freeze-and-thaw
STOFIT

Units
 Length Bohr
end

Atoms
 He   0.000000  0.000000  6.019000 f=He
 C    0.000000  0.000000  0.000000 f=co2
 O   -2.192000  0.000000  0.000000 f=co2
 O    2.192000  0.000000  0.000000 f=co2
end

Fragments
 He   t21.He
 co2  t21.co2.0  type=fde
   fdeoptions RELAX USEBASIS
 SubEnd
End

NOSYMFIT

integration 5.0

xc
 GGA pw91
end

FDE
 PW91K
 FULLGRID
 RELAXCYCLES 3
end

End Input
eor
eor

The example continues with the same calculation where partly the SAOP potential is used.