There are four required input sections for eT:
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.
Specifies the name of the calculation, which is printed in the output file.
Specifies the charge of the system.
Specifies the spin multiplicity of the system.
Enforce cartesian Gaussians basis functions for all atoms. Default for Pople basis sets.
Enforce spherical Gaussian basis functions for all atoms. Default for all basis sets except Pople basis sets.
Libint always returns cartesian p-orbitals.
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
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.
At the Hartree-Fock level of theory the following keywords may be specified:
hffor restricted Hartree-Fock (RHF)
mlhffor multilevel Hartree-Fock
uhffor unrestricted Hartree-Fock
In coupled cluster calculations, either RHF or MLHF must be specified, in addition to the coupled cluster method.
The available coupled cluster methods are:
For a Hartree-Fock calculation, specify the type of wavefunction (
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 section is where the type of calculation is specified. It will determine the \(e^T\) engine used in the calculation.
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.
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.
Keyword to run a ground state calculation at the level of theory given in the
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.
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.
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.
Keyword to run a coupled cluster excited state calculation. Enables the excited state engine, which calculates the ground and excited state amplitudes.
cc es solver section is required for excited state calculations.
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.
cc response section is required for coupled cluster response calculations.
Global restart keyword to activate restart where possible.
eT will first check if restart is possible and use the default start guess if not.
time dependent state
Keyword to run coupled cluster time propagation. Enables the time-dependent engine.
cc td section is required for coupled cluster time propagation.
To calculate the CCSD ground and four excited states, specify
do excited state end do
method hf ccsd end method
solver cc es singlet states: 4 end solver cc es
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
Possible values are
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
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
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 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