Searching....

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 angles Values in degrees, $0\leq value\leq 180$; atom2 is the middle atom of the bend: bend atom1 atom2 atom3 value out-of-plane-bends Values in degrees, $-180\leq value\leq 180$ atom2; angle between atom4 and the atom1–atom2–atom3 plane: outp atom1 atom2 atom3 atom4 value dihedral angles Values in degrees, $-180\leq value\leq 180$; angle the plane atom1–atom2–atom3 makes with the plane atom2–atom3–atom4: tors atom1 atom2 atom3 atom4 value coplanar bends Values in degrees, $-180\leq value\leq 180$; bending of atom1–atom2–atom3 in the plane atom2–atom3–atom4: linc atom1 atom2 atom3 atom4 value perpendicular bends Values in degrees, $-180\leq value\leq 180$; 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