To run an MLCC2 or MLCCSD calculation, the method mlcc2/mlccsd
must be specified in the method section.
E.g. for MLCC2
method
hf
mlcc2
end method
As multilevel methods are especially suited for intensive properties, its most relevant usage is for excited state calculations:
do
excited state
end do
The mlcc section is necessary for every MLCC calculation, it is used to specify how the active space is generated. E.g., for MLCC2 with approximated correlated natural transition orbitals (CNTOs) tailored for the lowest excited state:
mlcc
levels: ccs, cc2
cc2 orbitals: cnto-approx
cnto states: {1}
end mlcc
For MLCCSD (CCS/CCSD) with approximated CNTOs tailored for the lowest excited state:
mlcc
levels: ccs, ccsd
ccsd orbitals: cnto-approx
cnto states: {1}
end mlcc
If Cholesky or Cholesky-PAO orbitals are used, an active atom space must also be defined through the active atoms section. In the example below for two waters, the first water is selected as active (atoms 1, 2, and 3)
system
name: 2 H2O
end system
method
hf
mlcc2
end method
do
excited state
end do
solver cc es
singlet states: 2
end solver cc es
mlcc
levels: ccs, cc2
cc2 orbitals: cholesky-pao
end mlcc
active atoms
selection type: range
cc2: [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
If the calculation exited successfully
(look for eT terminated successfully! at the bottom of the file),
a summary of the excited state calculation should be printed at the end of the mlcc2.out file
...
- Electronic excitation energies:
Excitation energy
------------------------------------------
State (Hartree) (eV)
---------------------------------------------------------------
1 0.222134776911 6.044595162993
2 0.275347045324 7.492574739770
---------------------------------------------------------------
eV/Hartree (CODATA 2014): 27.21138602
- Finished solving the MLCC2 excited state equations (right)
...