Required input sections

There are four required input sections for eT:

  • system

  • method

  • do

  • geometry

system

In the system section of the input the name, charge, and multiplicity of the system is given. Furthermore, the use of cartesian Gaussians may be specified in this section.

Required keywords

name: [string]

Default: none

Specifies the name of the calculation, which is printed in the output file.

Optional keywords

charge: [integer]

Default: \(0\)

Specifies the charge of the system.

multiplicity: [integer]

Default: \(1\)

Specifies the spin multiplicity of the system.

cartesian gaussians

Default: false

Enables cartesian Gaussians basis functions.

Examples

A minimal example of the system section, includes only the name of the calculation. This can be any string, e.g.,

system
   name: water
end system

The charge and multiplicity is given in the example below. Additionally, cartesian Gaussians are enabled.

system
   name: water
   charge: 0
   multiplicity: 1
   cartesian gaussians
end system

method

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

Hartree-Fock methods

At the Hartree-Fock 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

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

  • mlcc2

Other methods

  • mp2

Examples

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

method
   hf
end method

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

method
   hf
   ccsd
end method

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.

ground state geoopt

Keyword to run a Hartree-Fock ground state geometry optimization. Enables the ground state geometry optimization engine.

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.

time dependent state

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

Note

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

Example

To calculate the CCSD ground and four excited states, specify

do
   excited state
end do

together with

method
   hf
   ccsd
end method

and

solver cc es
   singlet states: 4
end solver cc es

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
end geometry

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
end geometry

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
end geometry

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]
end geometry

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]
end geometry