### 18.3 How to Perform

##### 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:

GP is the integral over a normalized Gaussian auxiliary basis function. Naux is the number of auxiliary basis functions with GP 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.

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..

##### LHF

To run a LHF calculations select:

\$dft
functional lhf
gridsize   3

This can be done using define (modified grid are not supported) and then run odft.

A more suitable procedure is the following:

• Do a Hartree–Fock calculation using dscf.
• Use the script lhfprep to prepare the control file (the old control file will be saved in control.hf and the molecular orbitals in mos.hf or in alpha.hf and beta.hf for the spin-unrestricted case). See lhfprep -help for options. Actually LHF can be started from any guessed orbitals, but if HF orbitals are used, a much faster convergence is expected. By default the script lhfprep will add/modify the control file with:
\$dft
functional lhf
gridtype   6
gridsize   3
\$lhf
off-diag on
num-slater off
asymptotic dynamic=1.d-3
slater-dtresh 1.d-9
slater-region     7.0 0.5 10.0 0.5
corrct-region             10.0 0.5
\$scfdump
\$scfiterlimit 30
\$scfconv 6
\$scfdamp start=0.000 step=0.500 min=0.50
\$scforbitalshift noautomatic
\$correction matrix-elements file=lhfcg
\$correction alpha matrix-elements file=lhfcg_alpha
\$correction beta matrix-elements file=lhfcg_beta

• Run odft.

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 test-integ to check if the selected grid is accurate enough for the employed basis-set, see page 659.

The options in the \$lhf group are:

off-diag on

The LHF exchange potential is computed (default);

off-diag off

The KLI exchange potential is computed (can be selected by lhfprep -kli).

num-slater on

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.

num-slater off

the Slater potential is computed using basis-sets. This leads to very fast calculations, but accurate results are obtained only for first-row elements or if an uncontracted basis set or a basis set with special additional contractions is used. This is the default.

asymptotic

for asymptotic treatment there are three options:

asymptotic off

No asymptotic-treatment 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 density-matrix convergence or if Rydberg virtual orbitals are of no interest.

asymptotic on

Full asymptotic-treatment and use of the numerical Slater in the near asymptotic-region. It can be selected by lhfprep -asy.

asymptotic dynamic=1.d-3

Automatic switching on (off) to the special asymptotic treatment if the differential density-matrix rms is below (above) 1.d-3. This is the default.

pot-file save

the converged Slater and correction potentials for all grid points are saved in the files slater.pot and corrct.pot, respectively. Using pot-file 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.

homo

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.

correlation func=functional

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 ??.