Example: FDE geometry optimization: NH3-H2O: FDE geometry optimization¶

Download GO_FDE_NH3-H2O.run

This examples performs a structure optimization of H₂ O in presence of frozen NH₃ (via optimization of selected coordinates) with LDA and DZ basis. We need a high accint of 6.0 here because the potential energy surface is rather flat and small errors might lead to discrepancies in final structures. It uses (at present) the old branch optimizer for this purpose.

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).

First, the NH₃ fragment is made. Next the FDE geometry optimization is performed with:

$ADFBIN/adf << eor
TITLE NH3-H2O dimer FDE LDA DZ structure optimization of H2O
STOFIT
ATOMS
      N     -1.01393958      -0.15260815       0.00000000    f=nh3
      H     -1.16290010      -1.15738765       0.00000000    f=nh3
      H     -1.49925696       0.21074929       0.81414267    f=nh3
      H     -1.49925696       0.21074929      -0.81414267    f=nh3
      O     Ox  Oy  Oz
      H     H1x H1y H1z
      H     H2x H2y H2z
END
GEOVAR
 Ox    2.25288687
 Oy   -0.00423586
 Oz    0.00000000
 H1x   1.28270504
 H1y   0.05211069
 H1z   0.00000000
 H2x   2.54788803
 H2y   0.90516678
 H2z   0.00000000
END
FRAGMENTS
 O t21.O_LDA_DZ
 H t21.H_LDA_DZ
 nh3 t21.NH3_LDA_DZ type=fde
END
FDE
 THOMASFERMI
END
XC
 LDA VWN
END
GEOMETRY
 Branch Old
 Optim Selected
 Iterations 100 ! (default is 30)
END
INTEGRATION 6.0 6.0 6.0
eor