What’s new

The following is a short summary of the most important changes in new releases of TBmodels, starting after version 1.1.

What’s new in TBmodels 1.4

New features

  • The KdotpModel has been promoted from an internal-only interface to the public tbmodels.kdotp submodule.

  • The supercell method can be used to obtain a supercell tight-binding model.

  • The hamilton and eigenval methods now also accept a list of k-points as input, returning a sequence of results in that case. This improves performance when evaluating many k-points.

  • The change_unit_cell method can be used to change the shape or origin of the unit cell. The unit cell volume must be kept the same, and the new unit cell must be compatible with the current lattice.

  • Add remove_small_hop and remove_long_range_hop methods to cut hoppings with small value or long distance, respectively. Both these methods operate in-place on the existing model.

  • When using pos_kind='nearest_atom', the from_wannier_files method (and by extension the from_wannier_folder method and parse command) have an additional check: The ratio between next-nearest and nearest distance can be no lower than a given distance_ratio_threshold. Note that this is a backwards-incompatible change, because the check might fail for cases where parsing succeeded before. However, we expect a failing check to indicate an underlying problem in most cases. To disable the check, set distance_ratio_threshold=1.

Command-line interface

  • Add --version option to the command-line interface, to print the current version.

  • Add a --verbose option to the command-line interface, which causes informational output to be printed. By default, the CLI is now silent.

  • The command-line interfaces creating tight-binding models support a --sparsity flag to change the sparsity of the output model (valid options are as_input, dense, and sparse). Setting --sparsity=sparse can significantly reduce the memory needed to store a model.

Experimental features

  • The fold_model method creates a tight-binding model for a smaller unit cell from a supercell model.

Deprecations and removals

  • The from_hr and from_hr_file methods, deprecated since version 1.1, have been removed.

  • The __repr__ of the model can no longer be evaluated to create a new model. This feature had led to problems because the resulting string can be very large.

What’s new in TBmodels 1.3

New features

  • Constructing k.p models: The construct_kdotp() method can be used to construct a k.p model from an existing tight-binding model.

  • Joining models: The join_models() method can be used to combine models of the same structure with different orbitals.

Other improvements

  • Efficiency: Empty hopping matrices are now automatically removed when constructing a new model. In some cases this can lead to significant performance improvements. No action is required to get these run-time benefits. To also reduce the size of existing models, they need to be loaded and saved.

Other changes

  • License: TBmodels is now released under the more permissive Apache license.

What’s new in TBmodels 1.2

New features

  • Symmetrization feature: The symmetrize() method allows symmetrizing tight-binding models by computing a group average, as described in this paper.

  • Command-line interface: A command-line interface for performing the most common tasks such as parsing models, symmetrizing, or evaluating bands was added.

  • Convenience function for Wannier90 parsing: The from_wannier_folder() method was added to conveniently parse the output of a Wannier90 calculation, without having to specify each individual file.

Other changes

  • Update HDF5 file format: The HDF5 file format was changed to be compatible with other tools in the Z2Pack ecosystem, such as symmetry-repesentation. The old format is still supported, so no action is required.