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120 lines
6.1 KiB
ReStructuredText
120 lines
6.1 KiB
ReStructuredText
.. _convW90:
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Wannier90 Converter
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===================
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Using this converter it is possible to convert the output of
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`wannier90 <http://wannier.org>`_
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Maximally Localized Wannier Functions (MLWF) and create a HDF5 archive
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suitable for one-shot DMFT calculations with the
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:class:`SumkDFT <dft.sumk_dft.SumkDFT>` class.
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The user must supply two files in order to run the Wannier90 Converter:
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#. The file :file:`seedname_hr.dat`, which contains the DFT Hamiltonian
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in the MLWF basis calculated through :program:`wannier90` with ``hr_plot = true``
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(please refer to the :program:`wannier90` documentation).
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#. A file named :file:`seedname.inp`, which contains the required
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information about the :math:`\mathbf{k}`-point mesh, the electron density,
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the correlated shell structure, ... (see below).
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Here and in the following, the keyword ``seedname`` should always be intended
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as a placeholder for the actual prefix chosen by the user when creating the
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input for :program:`wannier90`.
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Once these two files are available, one can use the converter as follows::
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from triqs_dft_tools.converters import Wannier90Converter
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Converter = Wannier90Converter(seedname='seedname')
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Converter.convert_dft_input()
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The converter input :file:`seedname.inp` is a simple text file with
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the following format (do not use the text/comments in your input file):
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.. literalinclude:: images_scripts/LaVO3_w90.inp
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The example shows the input for the perovskite crystal of LaVO\ :sub:`3`
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in the room-temperature `Pnma` symmetry. The unit cell contains four
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symmetry-equivalent correlated sites (the V atoms) and the total number
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of electrons per unit cell is 8 (see second line).
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The first line specifies how to generate the :math:`\mathbf{k}`-point
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mesh that will be used to obtain :math:`H(\mathbf{k})`
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by Fourier transforming :math:`H(\mathbf{R})`.
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Currently implemented options are:
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* :math:`\Gamma`-centered uniform grid with dimensions
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:math:`n_{k_x} \times n_{k_y} \times n_{k_z}`;
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specify ``0`` followed by the three grid dimensions,
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like in the example above
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* :math:`\Gamma`-centered uniform grid with dimensions
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automatically determined by the converter (from the number of
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:math:`\mathbf{R}` vectors found in :file:`seedname_hr.dat`);
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just specify ``-1``
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Inside :file:`seedname.inp`, it is crucial to correctly specify the
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correlated shell structure, which depends on the contents of the
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:program:`wannier90` output :file:`seedname_hr.dat` and on the order
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of the MLWFs contained in it. In this example we have four lines for the
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four V atoms. The MLWFs were constructed for the t\ :sub:`2g` subspace, and thus
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we set ``l`` to 2 and ``dim`` to 3 for all V atoms. Further the spin-orbit coupling (``SO``)
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is set to 0 and ``irep`` to 0.
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As in this example all 4 V atoms are equivalent we set ``sort`` to 0. We note
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that, e.g., for a magnetic DMFT calculation the correlated atoms can be made
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inequivalent at this point by using different values for ``sort``.
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The number of MLWFs must be equal to, or greater than the total number
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of correlated orbitals (i.e., the sum of all ``dim`` in :file:`seedname.inp`).
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If the converter finds fewer MLWFs inside :file:`seedname_hr.dat`, then it
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stops with an error; if it finds more MLWFs, then it assumes that the
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additional MLWFs correspond to uncorrelated orbitals (e.g., the O-\ `2p` shells).
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When reading the hoppings :math:`\langle w_i | H(\mathbf{R}) | w_j \rangle`
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(where :math:`w_i` is the :math:`i`-th MLWF), the converter also assumes that
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the first indices correspond to the correlated shells (in our example,
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the V-t\ :sub:`2g` shells). Therefore, the MLWFs corresponding to the
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uncorrelated shells (if present) must be listed **after** those of the
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correlated shells.
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With the :program:`wannier90` code, this can be achieved by listing the
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projections for the uncorrelated shells after those for the correlated shells.
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In our `Pnma`-LaVO\ :sub:`3` example, for instance, we could use::
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Begin Projections
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V:l=2,mr=2,3,5:z=0,0,1:x=-1,1,0
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O:l=1:mr=1,2,3:z=0,0,1:x=-1,1,0
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End Projections
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where the ``x=-1,1,0`` option indicates that the V--O bonds in the octahedra are
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rotated by (approximatively) 45 degrees with respect to the axes of the `Pbnm` cell.
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The last line of :file:`seedname.inp` is the DFT Fermi energy (in eV), which is subtracted from the onsite terms in the :file:`seedname_hr.dat` file. This is recommended since some functions in DFTTools implicitly assume a Fermi energy of 0 eV.
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The converter will analyse the matrix elements of the local Hamiltonian
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to find the symmetry matrices `rot_mat` needed for the global-to-local
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transformation of the basis set for correlated orbitals
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(see section :ref:`hdfstructure`).
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The matrices are obtained by finding the unitary transformations that diagonalize
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:math:`\langle w_i | H_I(\mathbf{R}=0,0,0) | w_j \rangle`, where :math:`I` runs
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over the correlated shells and `i,j` belong to the same shell (more details elsewhere...).
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If two correlated shells are defined as equivalent in :file:`seedname.inp`,
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then the corresponding eigenvalues have to match within a threshold of 10\ :sup:`-5`,
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otherwise the converter will produce an error/warning.
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If this happens, please carefully check your data in :file:`seedname_hr.dat`.
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This method might fail in non-trivial cases (i.e., more than one correlated
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shell is present) when there are some degenerate eigenvalues:
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so far tests have not shown any issue, but one must be careful in those cases
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(the converter will print a warning message).
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The current implementation of the Wannier90 Converter has some limitations:
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* Since :program:`wannier90` does not make use of symmetries (symmetry-reduction
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of the :math:`\mathbf{k}`-point grid is not possible), the converter always
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sets ``symm_op=0`` (see the :ref:`hdfstructure` section).
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* No charge self-consistency possible at the moment.
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* Calculations with spin-orbit (``SO=1``) are not supported.
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* The spin-polarized case (``SP=1``) is not yet tested.
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* The post-processing routines in the module
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:class:`SumkDFTTools <dft.sumk_dft_tools.SumkDFTTools>`
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were not tested with this converter.
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* ``proj_mat_all`` are not used, so there are no projectors onto the
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uncorrelated orbitals for now.
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