H₂O: constraint Linear Transit

Sample directory: adf/LT_constraint/

The LINEARCONSTRAINTS keyword allows geometry optimizations (old branch) with constraints defined by arbitrary linear combinations of (internal) coordinates. The constraint has to be satisfied at the start of the geometry optimization. Note that the before ADF2008.01 the key LINEARCONSTRAINTS was called CONSTRAINT.

Example for bond length constraint, where at the start of the linear transit rOH1=R1=1.0, and rOH2=R2=1.5, such that (-1.0)*R1+(1.0)*R2=0.5, and in the final geometry -R1+R2=0.0 (Reactcoord 0.5 0.0)

$ADFBIN/adf << eor
title constraint keyword
XC
  GGA Becke Perdew
END

Geometry
 Branch Old
 LinearTransit  6
End

Integration 5.0 

Atoms Internal
O  0 0 0                
H  1 0 0    R1
H  1 2 0    R2  109.9
End

GeoVar
 R1 =1.
 R2 =1.5
End

LinearConstraints
 ReactCoord 0.5 0.0 
  R1  -1.0
  R2   1.0
 SubEnd
End

Basis
 Type DZP
End

end input
eor