Initialization of Force Constant Matrices

The most simple initial hessian is a unit matrix. However, better choices are preferable. For structure optimizations using internal coordinates you may use structural information to set up a diagonal force constant matrix with elements chosen in accord to the softness or stiffness of the individual modes. For detailed information refer to ref. [31]. For optimization of basis set parameters less information is available. When neither data block $forceapprox is available nor $forceinit on is set, the force constant matrix will be initialized as a unit matrix. Specifying the force constant initialization key $forceinit on diag=... will lead to:

diag=real

Initialization with real as diagonal elements.

diag=default

Initial force constant diagonals will be assigned the following default values:

internal coordinates : stretches 0.50

angles 0.20

scaling factors : s,p 1.50

d 3.00

exponents : uncontracted 0.15

contracted 10.00

contraction coefficients : 100.00

global scaling factor : 15.00

cartesian force constants : 0.50

diag=individual

Initial force constant diagonals will be taken from
$intdef fdiag=... or
$global fdiag=...
Similar initialization modes are NOT supported for geometry optimization in cartesian space and for the optimization of basis set parameters!

carthess

Data group $hessian (projected) is used.