A **geometry optimization** is automatically carried out, as soon as s are specified in the
Z-Matrix after the variable names.

The **default choice** is a search for a **minimum** on the potential energy surface
using **analytically evaluated gradients** within a **Quasi-Newton scheme**. The Hessian
update is then done using the **BFGS scheme** starting with a unit matrix in the first iteration.

If a Hessian matrix is available, a **Newton-Raphson scheme** is applied.

A Powell-update of the Hessian (instead of the BGFS update) is performed when **GEO_METHOD=RFA** is specified.
A transition-state search is requested via **GEO_METHOD=TS** (for a detailed
description how transition states can be determined, see the corresponding example and recommendations)

The convergence criterium for completion is set via **GEO_CONV=N**. The value
is specified in Hartree/bohr and the default is **N=5** leading to a threshold value of 10**-5.

The maximum number of iterations is specified via **GEO_MAXCYC**. Default
is here 50.

It is in many cases advantageous to perform the geometry optimization using a **pre-calculated force-constant matrix**. Such a force-constant matrix can be supplied by
simply copying the corresponding **FCM** or **FCMINT** file into the working directory.
Another option is to compute the force-constant matrix within the same job at the same
or at a lower level than the actual geometry optimization. This can be accomplished by
specifying a **%fcm** section in the **ZMAT** file which contains all the relevant
information for this preceeding force-constant calculation.

**Examples**

*geometry optimizations based on analytic gradients*

*geometry optimizations based on single-point energies*

*transition-state search using analytic gradients*

**Recommendations to Geometry Optimizations**