This option allows you to use a cartesian hessian matrix, computed in a FREQUENCIES calculation as a starting guess to the Hessian in a geometry-optimization. The Hessian is transformed automatically into the coordinate system the optimization is performed in. This option might be very useful in transition state optimization, i.e. by using a cheap analytical SCF Hessian as a starting guess to a higher level optimization (See example hcn_mp2_ts.com below).
The starting hessian is read from record irec on file ifil (compare the SAVE subcommand of FREQUENCIES, section 30.4ff.). If no irec.ifil is given, the last FREQ record found on file ifil=2 will be used.
Note that the HSTART option has lower priority than the NUMHES card. If NUMHES is given, any HSTART command will be ignored.
Input: hcn_mp2_ts.com Output: hcn_mp2_ts.out