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 :
stre atom1 atom2 value
angles
Values in degrees, ; atom2 is the middle atom
of the bend:
bend atom1 atom2 atom3 value
out-of-plane-bends
Values in degrees, atom2; angle between
atom4 and the atom1–atom2–atom3 plane:
outp atom1 atom2 atom3 atom4 value
dihedral angles
Values in degrees, ; angle the plane
atom1–atom2–atom3 makes with the plane atom2–atom3–atom4:
tors atom1 atom2 atom3 atom4 value
coplanar bends
Values in degrees, ; bending of
atom1–atom2–atom3 in the plane atom2–atom3–atom4:
linc atom1 atom2 atom3 atom4 value
perpendicular bends
Values in degrees, ; 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.
$molecule 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 $end $rem JOBTYPE opt METHOD hf BASIS 3-21g GEOM_OPT_PRINT 6 $end $opt CONSTRAINT stre 1 6 1.8 bend 2 1 4 110.0 bend 2 1 5 110.0 ENDCONSTRAINT $end