OEP-EXX

To run OEP-EXX calculations select:

$dft functional oep

As the computation of the OEP functional is completely analytic and grid free, any selection of a grid type or size will not influence the OEP calculation in contrast to other density functionals.

Particular care is instead required to orbital and auxiliary basis set.
An arbitrary combination of them can lead to very good total energy (i.e. very close to the Hartree-Fock one) but unphysical
OEP potential.
In the present release we strongly recommend to use the *d-aug-cc-pVTZ-oep* basis set and the corresponding auxiliary basis set
(directory `xbasen`

).

The following options can modify the quality, time and output of an OEP calculation.
All the options can be set by `define`.

Every option has a reasonable default value so the user does not need to select any of the options below to run a proper OEP calculation.

`$oep`*options*-

Listing of all possible options for the flag`$oep`

.`charge vector`*integer*-

The Charge condition expansion coefficients in auxiliary basis set representation can be calculated in different kinds.

The selection ofwill use the following ansatz to calculate the coefficients:*integer*= 1*c*_{P1}=

is the integral over a normalized Gaussian auxiliary basis function.*G*_{P}is the number of auxiliary basis functions with*N'*_{aux}.*G*_{P}≠ 0

The selection ofwill use the following ansatz to calculate the coefficients:*integer*= 2*c*_{P2}=

The variable

*integer*must have an integer value. The default value is`2`. `condition`[*string2*]*string*-

In the OEP method two constraints can be applied in the OEP equation. This is the HOMO condition and the Charge condition. The variable*string*can have the values`none`,`HOMO`,`Charge`and`both`. No condition is chosen when`none`is elected. The HOMO condition is chosen when`HOMO`is elected. The Charge condition is chosen when`Charge`is elected. The HOMO condition and the Charge condition are chosen when`both`is elected.

The variable*string2*is optional and only electable if a spin-unrestric-ted calculation is performed. The variable*string2*can have the values`alpha`and`beta`. If*string2*=`alpha`then the condition is defined for the alpha spin channel. If*string2*=`beta`then the condition is defined for the beta spin channel. Both spin channels can have different values.

Example:

$oep condition alpha HOMO condition beta Charge

If only one spin channel is defined the other spin channel uses the same condition automatically. The default value in any case is*string*=`both`. `core memory`*integer*-

Core memory is the amount of main memory given to the OEP calculation to store the three index integrals calculated during the OEP calculation. The core memory amount is given MB. The calculation runs as fast as possible if all three index integrals can be stored in the core memory. The variable*integer*must have an integer value. The default value is`200`. `debug`-

Print further information about the OEP calculation especially matrices and vectors used during the OEP calculation. Use this option carefully since a lot of data is written. The default value is`.false.`. `eigenvalue difference`*integer*-

Two molecular orbitals are considered as degenerated (due to symmetry or incidentally), if the difference between them is smaller then**10**. The variable^{-integer}*integer*must have an integer value. The default value is`6`. `plot coefficient`*string*-

The expansion coefficients for the auxiliary basis functions which build the local exact exchange potential are written to the file`oepcVx.dat`or in case of a spin-unrestricted calculation to the files`oepcVxa.dat`and`oepcVxb.dat`.

If*string*is`cartesian`the expansion coefficients are given for a cartesian atomic orbital auxiliary basis, if*string*equals`spherical`the expansion coefficients are given for a spherical atomic orbital auxiliary basis. In any case the expansion coefficients are given for the single atomic orbital auxiliary basis function and contain no information about the symmetry of the system (c1 case). The default value is`cartesian`. `reference potential`-

Use the reference potential constructed by the applied conditions to the OEP calculation as exchange potential. The solution of the OEP equation is skipped. The default value is`.false.`.