Multilevel Hartree-Fock calculation

Setting up an MLHF calculation

To run an MLHF calculation, the method mlhf must be specified in the method section.

method
   mlhf
end method

Furthermore, you must request a ground state calculation in the do section.

do
  ground state
end do

As MLHF calculations run in the MO basis, it is also necessary to specify the mo-scf-diis algorithm in the solver scf keyword section.

solver scf
   algorithm: mo-scf-diis
end solver scf

Additionally, an active atom space has to be defined through the active atoms section. In this section a selection type has to be chosen. The options are list, range and central atom. For MLHF this keyword is followed by the keyword hf (for Hartree-Fock) where the active atoms are specified. For the selection type list a list of numbers has to be specified where each number refers to an atom in the geometry. For the selection type range 2 numbers has to be specified where each number refers to an atom in the geometry. All atoms from the first to the second number are selected. For the selection type: central atom one atom central atom is chosen by giving a number to the central atom keyword. The active atoms are chosen depending on the range from this central atom. The range is given as floating point number in the hf keyword.

A minimal working example for an MLHF single-point calculation on 2 water molecules can be found below. The first water molecule (atoms 1, 2 and 3) is selected as active while the other water molecule is inactive.

system
   name: 2 waters
end system

 method
    mlhf
 end method

do
   ground state
end do

solver scf
   algorithm: mo-scf-diis
end solver scf

active atoms
   selection type: range
   hf: [1,3]
end active atoms

geometry
basis: aug-cc-pVDZ
H          0.86681        0.60144        5.00000
H         -0.86681        0.60144        5.00000
O          0.00000       -0.07579        5.00000
H          0.86681        0.60144        0.00000
H         -0.86681        0.60144        0.00000
O          0.00000       -0.07579        0.00000
end geometry

Save this as 2_waters.inp and type the following command in your terminal (here shown for four threads)

eT_launch --omp 4

After the calculation finished you should find 2_waters.out and 2_waters.timing.out in your working directory. Obtaining the timing file can be suppressed by specifying the -nt flag after eT_launch. If the calculation exited successfully (look for eT terminated successfully! at the bottom of the file), the output file should show iteration information for the solver converging the MLHF equations. The table with the iteration information should end with something like this:

...
  7          -151.950133335899     0.1229E-04     0.3615E-08
  8          -151.950133335979     0.1492E-05     0.8060E-10
  9          -151.950133335983     0.3509E-06     0.3524E-11
---------------------------------------------------------------
Convergence criterion met in 9 iterations!

An optional multilevel hf section can be specified in an MLHF calculation to request specific settings such as generating Cholesky active virtual orbitals, an initial full space HF optimization to a given threshold, or a projection on a minimal basis. In this last case, the section would look like the following example:

multilevel hf
   project on minimal basis
end multilevel hf