Required input sections¶

There are three required input sections for eT:

method
do
geometry

method¶

In the method section, the wave function method is specified. In the case of a post-HF calculation, both the reference wave function method and the post-HF method must be specified.

Self-Consistent Field methods¶

At the Self-Consistent Field level of theory the following keywords may be specified:

hf for restricted Hartree-Fock (RHF)
mlhf for multilevel Hartree-Fock
uhf for unrestricted Hartree-Fock
rohf for restricted open-shell Hartree-Fock
cuhf for constrained unrestricted Hartree-Fock
qed-hf for quantum electrodynamics Hartree-Fock (QED-HF)
sc-qed-hf for strong coupling quantum electrodynamics Hartree-Fock (SC-QED-HF)
dft for density functional theory (DFT)

In coupled cluster calculations, either RHF or MLHF must be specified, in addition to the coupled cluster method.

Coupled cluster methods¶

The available coupled cluster methods are:

ccs
cc2
lowmem-cc2
ccsd
ccsd(t)
cc3
ccsdt
mlcc2
mlccsd
qed-ccsd

Other methods¶

mp2
fci
casci
fci
qed-fci

Examples¶

For a Hartree-Fock calculation, specify the type of wave function (hf, mlhf, or uhf) in the method section.

- method
   hf

To perform a coupled cluster calculation, both the coupled cluster method and the type of reference wave function must be specified.

- method
   hf
   ccsd

do¶

The do section is where the type of calculation is specified. It will determine the \(e^T\) engine used in the calculation.

Note

Only one of the keywords below has to be specified. For example for the calculation of excited states only the keyword excited state is required even though the ground state equations have to be solved as well to obtain excited states.

Keywords¶

cholesky eri

Keyword to run a Cholesky decomposition of the two-electron integrals. Note that this is done automatically for any coupled cluster calculation, the keyword should only be given if only Cholesky decomposition is to be performed.

ground state

Keyword to run a ground state calculation at the level of theory given in the method section. Enables the ground state or reference engine.

geometry optimization

Keyword to run a geometry optimization. Enables the geometry optimization engine. Only ground state optimizations are available for HF, while excited state optimized structures are also available at the CC level of theory. Depending on the availability, the optimization will be performed with analytical gradients (available for HF and CCSD) or numerical gradients (if analytical is not available).

harmonic frequencies

Keyword to determine vibrational frequencies and normal modes for HF and CC methods. Recommended to use for methods that have analytical gradients (HF and CCSD). A default calculation determines the frequencies and the normal modes. See harmonic frequencies section for additional calculations (such as Wigner sampling).

mean value

Keyword to calculate coupled cluster expectation values. Enables the mean value engine, which determines the coupled cluster ground state amplitudes and multipliers, and calculates the requested expectation value. Which mean value(s) to calculate are specified in the cc mean value section.

Note

For Hartree-Fock calculations, one must write ground state in do and specify the mean value(s) to calculate in the hf mean value section.

excited state

Keyword to run a coupled cluster excited state calculation. Enables the excited state engine, which calculates the ground and excited state amplitudes.

Note

The cc es solver section is required for excited state calculations.

response

Keyword to enable the coupled cluster response engine. Implemented features are EOM transition moments and polarizabilities for CCS, CC2, CCSD and CC3, and LR transition moments and polarizabilities for CCS. The response engine drives the calculation of ground state amplitudes and multipliers, excited state vectors (left and right eigenvectors of the Jacobian matrix) and the requested property.

Note

The cc response section is required for coupled cluster response calculations.

restart

Global restart keyword to activate restart where possible.

Note

eT will first check if restart is possible and use the default start guess if not.

real time

Keyword to run coupled cluster time propagation. Enables the time-dependent engine.

Note

The cc real time section is required for coupled cluster time propagation.

shielding

Keyword to run CPHF nuclear shielding tensors.

tdhf excited state

Keyword to run TDHF excitation energies (Tamm-Dancoff or RPA).

Note

The solver tdhf es section is required for TDHF excited state calculations.

tdhf response

Keyword to run TDHF response calculation (polarizabilities).

Example¶

To calculate the CCSD ground and four excited states, specify

- do
  excited state

together with

- method
  hf
  ccsd

and

- solver cc es
  singlet states: 4

geometry¶

The geometry must be given as xyz coordinates either with Angstrom or Bohr units. The default units are Angstrom. The basis set is also given in the geometry section.

Minimal example for the geometry section

- 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

If other units than Angstrom are desired, this must be specified at the top of the geometry section with the units keyword. Possible values are Angstrom and Bohr.

- geometry
   units: Bohr
   basis: aug-cc-pVDZ
   H          1.63803   1.13655   9.44863
   H         -1.63803   1.13655   9.44863
   O          0.00000  -0.14322   9.44863

Different basis sets may be placed on the atoms using the basis keyword. An atom is given the last basis set specified above it, e.g. in the following example the oxygen has the d-aug-cc-pVDZ basis and the hydrogens have the aug-cc-pVDZ basis. See here for a list of included basis sets.

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

Basis functions can be placed without the corresponding atom by using the keyword ghost. Every atom specified after the keyword will have zero charge, which corresponds to only placing the basis functions at the specified location. An H2 calculation run with the same basis functions as H2O can be done using this geometry:

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

In case of QM/MM calculations, the QM and MM portions have to be separated by a line containing --. The parameters for QM/MM calculations are placed after the XYZ coordinates. In case of electrostatic QM/MM embedding (see molecular mechanics section), the charge of each atom needs to be provided:

- geometry
   basis: cc-pVDZ
    O      0.87273600      0.00000000     -1.24675400
    H      0.28827300      0.00000000     -2.01085300
    H      0.28827300      0.00000000     -0.48265500
    --
    O [IMol=   1]     -0.77880300      0.00000000      1.13268300      [q=-0.834]
    H [IMol=   1]     -0.66668200      0.76409900      1.70629100      [q=+0.417]
    H [IMol=   1]     -0.66668200     -0.76409900      1.70629000      [q=+0.417]

In case of polarizable QM/FQ (see molecular mechanics section), the electronegativities (chi) and chemical hardnesses (eta) are needed for each atom:

- geometry
   basis: cc-pVDZ
    O      0.87273600      0.00000000     -1.24675400
    H      0.28827300      0.00000000     -2.01085300
    H      0.28827300      0.00000000     -0.48265500
    --
    O [IMol=   1]     -0.77880300      0.00000000      1.13268300     [chi=0.11685879436,eta=0.58485173233]
    H [IMol=   1]     -0.66668200      0.76409900      1.70629100     [chi=0.00000000000,eta=0.62501048888]
    H [IMol=   1]     -0.66668200     -0.76409900      1.70629000     [chi=0.00000000000,eta=0.62501048888]