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9.4 Constrained Optimization

9.4.2 Geometry Optimization with General Constraints

(May 7, 2024)

CONSTRAINT and ENDCONSTRAINT define the beginning and end, respectively, of the constraint section of $opt within which users may specify up to six different types of constraints:

interatomic distances
Values in Ångstroms; value >0:
stre   atom1   atom2   value

Values in degrees, 0value180; atom2 is the middle atom of the bend:
bend   atom1   atom2   atom3   value

Values in degrees, -180value180 atom2; angle between atom4 and the atom1–atom2–atom3 plane:
outp   atom1   atom2   atom3   atom4   value

dihedral angles
Values in degrees, -180value180; angle the plane atom1–atom2–atom3 makes with the plane atom2–atom3–atom4:
tors   atom1   atom2   atom3   atom4   value

coplanar bends
Values in degrees, -180value180; bending of atom1–atom2–atom3 in the plane atom2–atom3–atom4:
linc   atom1   atom2   atom3   atom4   value

perpendicular bends
Values in degrees, -180value180; bending of atom1–atom2–atom3 perpendicular to the plane atom2–atom3–atom4:
linp   atom1   atom2   atom3   atom4   value

Example 9.11  Methanol geometry optimization with constraints in bond length and bond angles.

   0  1
   C   0.14192   0.33268   0.00000
   O   0.14192  -1.08832   0.00000
   H   1.18699   0.65619   0.00000
   H  -0.34843   0.74268   0.88786
   H  -0.34843   0.74268  -0.88786
   H  -0.77395  -1.38590   0.00000

   JOBTYPE           opt
   METHOD            hf
   BASIS             3-21g

   stre  1  6  1.8
   bend  2  1  4  110.0
   bend  2  1  5  110.0