36.2.16 Hessian starting guess from a frequency calculation (HSTART)

HSTART,irec.ifil;

This option allows you to use a cartesian hessian matrix, computed in a FREQUENCIES calculation (or using the cpmcscf,hessian option in multi) 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). Note that dummy atoms are ignored, and therefore the coordinates of dummy atoms should not depend on variables.

The starting hessian is read from record irec on file ifil (compare the SAVE subcommand of FREQUENCIES, section 33ff.). If no irec.ifil is given, the last FREQ record found on file ifil=2 will be used.

Note that the HSTART option has higher priority than the NUMHES card. If a hessian is found using the HSTART command, the NUMHES command will be ignored.

Further note that if the hessian is read from file 1, it is assumed that it has been calculated at the current geometry and the hessian update is disabled. On the other hand, if the hessian is found on file 2 or 3, it is assumed that it has only been computed in the first iteration, and the hessian update is performed in subsequent iterations.

Input: hcn_mp2_ts.com

Output: hcn_mp2_ts.out