mirror of
https://github.com/triqs/dft_tools
synced 2024-11-12 17:13:48 +01:00
c4db7e6867
* remove manual module reference files * move hdf5 structure reference to guide * fix various doc strings * remove very old update_archive python script for triqs 1.2 * refine main documentation.rst file -> better overview
54 lines
4.7 KiB
ReStructuredText
54 lines
4.7 KiB
ReStructuredText
.. _soc:
|
|
|
|
Spin-orbit coupled calculations (single-shot)
|
|
=============================================
|
|
|
|
There are two main ways of including the spin-orbit coupling (SOC) term into
|
|
DFT+DMFT calculations:
|
|
|
|
- by performing a DFT calculation including SOC and then doing a DMFT calculation on top, or
|
|
- by performing a DFT calculation without SOC and then adding the SOC term on the model level.
|
|
|
|
The second variant is a bit more involved and needs quite some expertise, so this guide will cover only the first variant with SOC included in the DFT calculations.
|
|
|
|
Treatment of SOC in DFT
|
|
-----------------------
|
|
|
|
For now, TRIQS/DFTTools does only work with Wien2k and Elk when performing calculations with SO.
|
|
The treatment of SOC in the VASP package is fundamentally different to the way Wien2k treats it, and the interface does not handle that at the moment.
|
|
Therefore, this guide describes how to do an SOC calculation using the Wien2k and Elk DFT packages.
|
|
|
|
Treatment of SOC in Wien2k
|
|
--------------------------
|
|
|
|
First, a Wien2k calculation including SOC has to be performed.
|
|
For details, we refer the reader to the `documentation of Wien2k <http://susi.theochem.tuwien.ac.at/reg_user/textbooks/>`_ . As a matter of fact, we need the output for the DFT band structure for both spin directions explicitly. That means that one needs to do a spin-polarised DFT calculation with SOC, but, however, with magnetic moment set to zero. In the Wien2k initialisation procedure, one can choose for the option -nom when ``lstart`` is called. This means that the charge densities are initialised without magnetic splitting. The SOC calculation is then performed in a standard way as described in the Wien2k manual.
|
|
|
|
Performing the projection in Wien2k
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Note that the final ``x lapw2 -almd -so -up`` and ``x lapw2 -almd -so -dn`` have to be run *on a single core*, which implies that, before, ``x lapw2 -up``, ``x lapw2 -dn``, and ``x lapwso -up`` have to be run in single-core mode (at least once).
|
|
|
|
In the ``case.indmftpr`` file, the spin-orbit flag has to be set to ``1`` for the correlated atoms.
|
|
For example, for the compound Sr\ :sub:`2`\ MgOsO\ :sub:`6`, with the struct file :download:`Sr2MgOsO6.struct <Sr2MgOsO6/Sr2MgOsO6.struct>`, we would, e.g., use the ``indmftpr`` file :download:`found here <Sr2MgOsO6/Sr2MgOsO6_SOC.indmftpr>`.
|
|
Then, ``dmftproj -sp -so`` has to be called.
|
|
As usual, it is important to check for warnings (e.g., about eigenvalues of the overlap matrix) in the output of ``dmftproj`` and adapt the window until these warnings disappear.
|
|
|
|
Note that in presence of SOC, it is not possible to project only onto the :math:`t_{2g}` subshell because it is not an irreducible representation.
|
|
|
|
Treatment of SOC in Elk
|
|
-------------------------
|
|
|
|
First, a Elk calculation including SOC has to be performed. For details, we refer the reader to the SOC Elk examples in Elk's example directory and `Elk manual <https//elk.sourceforge.net/elk.pdf>`_ for further information about the input flags. Then the projectors can be generated using the ``wanproj`` input flag in the same format as in :ref:`convElk`. Like in Wien2k, you cannot project only onto the :math:`t_{2g}` subshell because it is not an irreducible representation in SOC calculations.
|
|
|
|
After generating the projectors
|
|
-------------------------------
|
|
|
|
We strongly suggest using the :py:meth:`.dos_wannier_basis` functionality of the :py:class:`.SumkDFTTools` class (see :download:`calculate_dos_wannier_basis.py <Sr2RuO4/calculate_dos_wannier_basis.py>`) and compare the Wannier-projected orbitals to the original DFT DOS (they should be more or less equal).
|
|
Note that, with SOC, there are usually off-diagonal elements of the spectral function, which can also be imaginary.
|
|
The imaginary part can be found in the third column of the files ``DOS_wann_...``.
|
|
|
|
After the projection, one can proceed with the DMFT calculation. However, two things need to be noted here. First, since the spin is not a good quantum number any more, there are off-diagonal elements in the hybridisation function and the local Hamiltonian coupling the two spin directions. This will eventually lead to a fermonic sign problem when QMC is used as a impurity solver. Second, although the :math:`e_{g}` subshell needs to be included in the projection, it can in many cases be neglected in the solution of the Anderson impurity model, after a transformation to a rotated local basis is done. This basis, diagonalising the local Hamiltonian in the presence of SOC, is often called the numerical j-basis. How rotations are performed is described in :ref:`basisrotation`, and the cutting of the orbitals in :ref:`blockstructure`.
|
|
|
|
A DMFT calculation including SOC for Sr2MgOsO6 using Wien2k is included in the :ref:`tutorials`.
|