A QED-Hartree-Fock (HF) calculation is performed by specifying a QED-HF (qed-hf) wave function
in the method section of the input file. To start a ground state
QED-HF we specify
- method
qed-hf
- do
ground state
A minimal working example for a QED-HF single-point calculation on water with wavevector \(\vec{k}=(0,0,1)\), frequency \(\omega=0.5\) au and coupling \(\lambda=0.05\) au:
- system
charge: 0
- do
ground state
- method
qed-hf
- boson
interaction type: photon
modes: 2
frequency: {0.5, 0.5}
wavevector: {0.0, 0.0, 1.0}
coupling: {0.05, 0.05}
- geometry
basis: cc-pVDZ
H 0.86681 0.60144 0.00000
H -0.86681 0.60144 0.00000
O 0.00000 -0.07579 0.00000
Save this as h2o.inp and invoke the launch script.
path/to/eT_launch.py h2o.inp
After the calculation finished you should find h2o.out and h2o.timing.out
in your working directory. If the calculation exited successfully
(look for eT terminated successfully! at the bottom of the file),
a summary of the calculation should be printed at the end.
The wave function has a coherent state parameter per each orbital in the basis that
diagonalizes the dipole operator. This way electron photon correlation is naturally
included in the methodology.
A Strong Coupling QED-Hartree-Fock (SC-QED-HF) calculation is performed by specifying a
SC-QED-HF (sc-qed-hf) wave function in the method section
of the input file. To start a ground state SC-QED-HF we specify
- method
sc-qed-hf
- do
ground state
A minimal working example for a SC-QED-HF single-point calculation on water with polarization \(\vec{\epsilon}=(0,0,1)\), frequency \(\omega=0.5\) au and coupling \(\lambda=0.05\) au:
- system
charge: 0
- do
ground state
- method
sc-qed-hf
- boson
interaction type: photon
modes: 1
frequency: {0.5}
polarization: {0.0, 0.0, 1.0}
coupling: {0.05}
- geometry
basis: cc-pVDZ
H 0.86681 0.60144 0.00000
H -0.86681 0.60144 0.00000
O 0.00000 -0.07579 0.00000
Save this as h2o.inp and invoke the launch script.
path/to/eT_launch.py h2o.inp
After the calculation finished you should find h2o.out and h2o.timing.out
in your working directory. If the calculation exited successfully
(look for eT terminated successfully! at the bottom of the file),
a summary of the calculation should be printed at the end.
A QED Full Configuration Interaction (FCI) calculation is performed by specifying a qed-hf/hf/sc-qed-hf
(for closed-shell systems) or a rohf/uhf wave function (for open-shell systems)
and the QED-FCI wave function (qed-fci) in the method section of the input file.
E.g., for a QED-HF calculation we write
- method
qed-hf
qed-fci
To perform a single-point QED-FCI calculation it is necessary to specify ground state do section:
- do
ground state
As in standard FCI the calculations require the solver ci section in which it is necessary to specify the number of states you want to compute in your calculation, for instance:
- solver fci
states: 5
A minimal working example for a QED-FCI single-point calculation on water with polarization \(\vec{\epsilon}=(0,0,1)\), frequency \(\omega=0.5\) au and coupling \(\lambda=0.05\) au:
- do
ground state
- memory
available: 16
- method
hf
fci
- boson
interaction type: photon
modes: 1
boson states: {1}
coupling: {0.05}
frequency: {0.5}
polarization: {0, 0, 1}
- solver fci
states: 5
- geometry
basis: sto-3g
H 0.86681 0.60144 0.00000
H -0.86681 0.60144 0.00000
O 0.00000 -0.07579 0.00000
Note
For open-shell calculations you might want to specify the multiplicity
in the system section. The default multiplicity is 1.
Save this as h2o.inp and invoke the launch script.
path/to/eT_launch.py h2o.inp
After the calculation finished you should find h2o.out and h2o.timing.out
in your working directory. If the calculation exited successfully
(look for eT terminated successfully! at the bottom of the file),
a summary of the calculation should be printed at the end.
It is also possible to perform QED-FCI calculations only in an active space of canonical molecular orbitals, leading to a Complete Active Space QED Configuration Interaction (QED-CASCI) calculation.
To perform a QED-CASCI calculation the keyword qed-fci needs to be exchanged with qed-casci in the method section. Similartly to QED-FCI, the QED-CASCI calculations can be computed using the QED-HF orbitals or the SC-QED-HF orbitals. This is specified by the qed-hf or sc-qed-hf wave function in the method section of the input file. E.g.,
- method
sc-qed-hf
qed-casci
Additionally, it is necessary to specify the number of active electrons and active canonical orbitals included in the active space. This is done using the canonical keyword in the active space section. For a CASCI calculation with 2 active electrons in 4 active canonical orbitals we write
- active space
canonical: {2, 4}
Warning
For a charged system, energy invariance under translation is not guaranteed if the QED-HF orbitals are employed. The use of the SC-QED-HF wave function is thus advised.