# *LOCALIZATION¶

Performs molecular orbitals localization using the Pipek-Mezey
criterion. The implementation uses an exponential parametrization and a
Trus region minimization method instead of the Edminston-Ruedenberg
algorithm. It works with the *C*_{1}symmetry and for the occupied orbitals.

## .PRJLOC¶

Localization from projection analysis instead of Mulliken analysis. [Default: False]:

`.PRJLOC`

## .OWNBAS¶

Calculate fragments in their own basis. For now it is the only option which can be used with projection analysis option (.PRJLOC) [Default: False]:

`.OWNBAS`

## .VECREF¶

First give number of fragments to project onto. Then for each fragment give
filename of MO coefficients and string specifying which orbitals will be
used in the projection (*Specification of orbital strings*):

```
.VECREF
3
DFO1AT
1..6
DFH1AT
1
DFH2AT
1
```

## .HESLOC¶

Define model of the Hessian [Default: FULL].

Use full Hessian:

```
.HESLOC
FULL
```

Use diagonal approximation of the Hessian. If using this approximation, there is danger of converging to the stationary point instead of minima:

```
.HESLOC
DIAG
```

First the diagonal approximation of the Hessian will be used and after reaching convergence criterion the localization will switch to the construction of the full Hessian:

```
.HESLOC
COMB
```

## .CHECK¶

This keyword can be used only in combination with .HESLOC = COMB. The full Hessian will be calculated only at the last iteration. This way one can check if the procedure converged to the minimum.

## .THFULL¶

Convergence threshold for the localization process. It applies on the functional value of the localization criteria when full Hessian is calculated. It is used in .HESLOC = FULL scheme and in the second part of the .HESLOC = COMB scheme. When not specified gradient criterion or criterion of the number of negative eigenvalues equals zero will be used:

```
.THFULL
1.0D-13
```

## .THGRAD¶

Convergence threshold for the localization process. It applies on the gradient of the localization functional. It is used in .HESLOC = FULL or DIAG scheme and in the second part of the .HESLOC = COMB scheme. When not specified the functional value criterion or criterion of the number of negative eigenvalues equals zero will be used:

```
.THGRAD
1.0D-17
```

## .THDIAG¶

Convergence threshold for the localization process. It applies on the functional value of the localization criteria when diagonal Hessian is calculated. It can be used with the .HESLOC = DIAG keyword. If .HESLOC = COMB it is used to switch from the first to the second stage of the convergence process:

```
.THDIAG
1.0D-05
```

## .SELECT¶

Select subset of MOs for localization (use *Specification of orbital strings* syntax).
Currently only Pipek-Mezey localization is implemented, therefore localize
only occupied orbitals. Localization of virtual orbitals is not recommended.

```
.SELECT
1..5
```