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`relax` drives and controls a non-linear optimization procedure to
locate the minimum (or a stationary point) of a function *f* (*x*). In
`TURBOMOLE` *f* is always the electronic energy, and the coordinates
*x* will be referred to as *general coordinates*. They include
- cartesian atomic coordinates
- internal atomic coordinates
- exponents, contraction coefficients and scaling factors of basis
functions
- a global scaling factor (a common scaling factor for all basis
set exponents)

The optimization employs an iterative procedure based on gradients
∇*f* of the current and, if available, previous iterations.
Various procedures can be applied: steepest descent, Pulay's
DIIS, quasi-Newton, conjugate
gradients, as well as combinations of them.
`relax` carries out:
- update of general coordinates
- update of approximate hessians if needed
- conversion of coordinates (internal
cartesian)

The mode of operation is chosen by the keywords `$optimize` and
`$interconversion` and the corresponding options, which will
be described in the following sections.

TURBOMOLE