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### 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 of integer = 1 will use the following ansatz to calculate the coefficients:  cP1 = GP is the integral over a normalized Gaussian auxiliary basis function. N'aux is the number of auxiliary basis functions with GP≠ 0 . The selection of integer = 2 will use the following ansatz to calculate the coefficients:  cP2 = 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-integer . The variable 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..

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