Initialization of the Hessian

Finally there are some options to control the choice of the initial Hessian during your geometry optimization:

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FORCE CONSTANTS INITIALIZATION OPTIONS FOR RELAX
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OPTION    | DESCRIPTION
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off       | switch off initialization (DEFAULT: on)
cart      | use analytical cartesian hessian provided by a
          | 2nd derivatives calculation. DEFAULT(n)
diag      | use diagonal matrix with diagonal elements set
          | individually within data groups $intdef or
          | $basis or $global. DEFAULT(n)
unit <r>  | use multiple of the unit matrix ( H = <r>*E ).
          | DEFAULT(n) - DEFAULT <r> =  1.000
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NOTE THAT THESE OPTIONS ARE MUTUALLY EXCLUSIVE
<RETURN> OR * OR q(uit) WILL TERMINATE THIS MENU

Option off will be used if you have already a good Hessian from a previous calculation which may be used. cart describes an even better state where you have a Hessian from a calculation of the second derivatives available (aoforce). The other two options describe real procedures for initialization of the Hessian. Default values: stretches (0.5), angles (0.2).