To run OEPEXX calculations select:
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 HartreeFock one) but unphysical OEP potential. In the present release we strongly recommend to use the daugccpVTZoep 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.
Listing of all possible options for the flag $oep.
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:

G_{P} is the integral over a normalized Gaussian auxiliary basis function. N′_{aux} is the
number of auxiliary basis functions with G_{P}≠0.
The selection of integer = 2 will use the following ansatz to calculate the
coefficients:

The variable integer must have an integer value. The default value is 2.
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–unrestricted 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:
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 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.
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..
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.
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.
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..
To run a LHF calculations select:
This can be done using define (modified grid are not supported) and then run odft.
A more suitable procedure is the following:
With the LHF potential Rydberg series of virtual orbitals can be obtained. To that end, diffuse orbital basis sets have to be used and special grids are required.
gridtype 4 is the most diffuse with special radial scaling; gridtype 5 is for very good Rydberg orbitals; gridtype 6 (default in Lhfprep) is the least diffuse, only for the first Rydberg orbitals.
Only gridsize 3–5 can be used, no modified grids.
Use testinteg to check if the selected grid is accurate enough for the employed basisset, see page 705.
The options in the $lhf group are:
The LHF exchange potential is computed (default);
The KLI exchange potential is computed (can be selected by lhfprep kli).
the Slater potential is calculated numerically everywhere: this is more accurate
but quite expensive. When ECPs are used, turn on this option. It can be
selected by lhfprep num.
the Slater potential is computed using basissets. This leads to very fast
calculations, but accurate results are obtained only for firstrow elements or if
an uncontracted basis set or a basis set with special additional contractions is
used. This is the default.
for asymptotic treatment there are three options:
No asymptotictreatment and no use of the numerical Slater. The
total exchange potential is just replaced by 1∕r in the asymptotic
region. This method is the fastest one but can be used only for the
densitymatrix convergence or if Rydberg virtual orbitals are of no
interest.
Full asymptotictreatment and use of the numerical Slater in the near
asymptoticregion. It can be selected by lhfprep asy.
Automatic switching on (off) to the special asymptotic treatment if the
differential densitymatrix rms is below (above) 1.d3. This is the default.
the converged Slater and correction potentials for all grid points are saved in the files
slater.pot and corrct.pot, respectively. Using potfile load, the
Slater potential is not calculated but read from slater.pot (the correction
potential is instead recalculated). For spin unrestricted calculations the
corresponding files are slaterA.pot, slaterB.pot, corrctA.pot and
correctB.pot.
allows the user to specify which occupied orbital will not be included in the
calculation of correction potential: by default the highest occupied orbital is selected.
This option is useful for those systems where the HOMO of the starting orbitals
(e.g. EHT, HF) is different from the final LHF HOMO. homob is for the beta
spin.
a correlation functional can be added to the LHF potential: use func=lyp for LYP, or
func=vwn for VWN5 correlation.
For other options see 19.3.