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146 lines
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146 lines
8.4 KiB
ReStructuredText
.. _analysis:
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Tools for analysis
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==================
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This section explains how to use some tools of the package in order to analyse the data.
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There are two practical tools for which a self energy on the real axis is not needed, namely:
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* :meth:`dos_wannier_basis <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools.dos_wannier_basis>` for the density of states of the Wannier orbitals and
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* :meth:`partial_charges <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools.partial_charges>` for the partial charges according to the :program:`Wien2k` definition.
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However, a real frequency self energy has to be provided by the user for the methods:
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* :meth:`dos_parproj_basis <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools.dos_parproj_basis>` for the momentum-integrated spectral function including self energy effects and
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* :meth:`spaghettis <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools.spaghettis>` for the momentum-resolved spectral function (i.e. ARPES)
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.. warning::
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This package does NOT provide an explicit method to do an **analytic continuation** of the
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self energies and Green functions from Matsubara frequencies to the real frequency axis!
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There are methods included e.g. in the :program:`ALPS` package, which can be used for these purposes.
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Keep in mind that all these methods have to be used very carefully!
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Initialisation
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--------------
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All tools described below are collected in an extension of the :class:`SumkDFT <pytriqs.applications.dft.sumk_dft.SumkDFT>` class and are
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loaded by importing the module :class:`SumkDFTTools <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools>`::
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from pytriqs.applications.dft.sumk_dft_tools import *
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The initialisation of the class is equivalent to that of the :class:`SumkDFT <pytriqs.applications.dft.sumk_dft.SumkDFT>`
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class::
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SK = SumkDFTTools(hdf_file = filename + '.h5')
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Note that all routines available in :class:`SumkDFT <pytriqs.applications.dft.sumk_dft.SumkDFT>` are also available here.
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If required, we have to load and initialise the real frequency self energy. Most conveniently,
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you have your self energy already stored as a real frequency :class:`BlockGf <pytriqs.gf.local.BlockGf>` object
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in a hdf5 file::
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ar = HDFArchive('case.h5', 'a')
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SigmaReFreq = ar['dmft_output']['Sigma_w']
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You may also have your self energy stored in text files. For this case we provide the function
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:meth:`constr_Sigma_real_axis`, which loads the data and puts it into a real frequency :class:`BlockGf <pytriqs.gf.local.BlockGf>` object::
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from pytriqs.applications.dft.build_sigma_from_txt import *
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SigmaReFreq = constr_Sigma_real_axis(SK, filename, hdf=False, hdf_dataset='SigmaReFreq',n_om=0, orb=0)
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where:
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* `filename`: the name of the hdf5 archive file or the `fname` pattern in text files names as described above,
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* `hdf`: if `True`, the real axis self energy will be read from the hdf5 file, otherwise from the text files,
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* `hdf_dataset`: the name of dataset where the self energy is stored in the hdf5 file,
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* `orb`: index of an inequivalent shell,
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* `n_om`: the number of points in the real-axis mesh (used only if `hdf=False`).
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It is important that you follow some rules concerning the structure of your data files:
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* Each data file should contain three columns: real frequency, real part and imaginary part of the self energy exactly in this order.
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* If all blocks of your self energy are of dimension 1x1, you store them in `filename_(block)0.dat` files. Here `(block)` is a block name (`up`, `down`, or combined `ud`).
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* In the case when you have matrix blocks, you store them in `(i)_(j).dat` files, where `(i)` and `(j)` are the zero based orbital indices, in the `filename_(block)` directory.
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Finally, we put the self energy into the `SK` object::
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SK.put_Sigma(Sigma_imp = [SigmaReFreq])
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and additionally set the chemical potential and the double counting correction from the DMFT calculation::
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chemical_potential, dc_imp, dc_energ = SK.load(['chemical_potential','dc_imp','dc_energ'])
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SK.set_mu(chemical_potential)
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SK.set_dc(dc_imp,dc_energ)
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del ar
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.. _dos_wannier:
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Density of states of the Wannier orbitals
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-----------------------------------------
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For plotting the density of states of the Wannier orbitals, you type::
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SK.dos_wannier_basis(broadening=0.03, mesh=[om_min, om_max, n_om], with_Sigma=False, with_dc=False, save_to_file=True)
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which produces plots between the real frequencies `om_min` and `om_max`, using a mesh of `n_om` points. The parameter
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`broadening` defines an additional Lorentzian broadening, and has the default value of `0.01 eV`. To check the Wannier
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density of states after the projection set `with_Sigma` and `with_dc` to `False`. If `save_to_file` is set to `True`
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the output is printed into the files
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* `DOS_wannier_(sp).dat`: The total DOS, where `(sp)` stands for `up`, `down`, or combined `ud`. The latter case
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is relevant for calculations including spin-orbit interaction.
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* `DOS_wannier_(sp)_proj(i).dat`: The DOS projected to an orbital with index `(i)`. The index `(i)` refers to
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the indices given in ``SK.shells``.
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* `DOS_wannier_(sp)_proj(i)_(m)_(n).dat`: As above, but printed as orbitally-resolved matrix in indices
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`(m)` and `(n)`. For `d` orbitals, it gives the DOS separately for, e.g., :math:`d_{xy}`, :math:`d_{x^2-y^2}`, and so on,
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otherwise, the ouptput is returned by the function for a further usage in :program:`python`.
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Partial charges
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---------------
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Since we can calculate the partial charges directly from the Matsubara Green's functions, we also do not need a
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real frequency self energy for this purpose. The calculation is done by::
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SK.put_Sigma(Sigma_imp = SigmaImFreq)
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dm = SK.partial_charges(beta=40.0, with_Sigma=True, with_dc=True)
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which calculates the partial charges using the self energy, double counting, and chemical potential as set in the
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`SK` object. On return, `dm` is a list, where the list items correspond to the density matrices of all shells
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defined in the list `SK.shells`. This list is constructed by the :program:`Wien2k` converter routines and stored automatically
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in the hdf5 archive. For the structure of `dm`, see also :meth:`reference manual <pytriqs.applications.dft.sumk_dft_tools.SumkDFTTools.partial_charges>`.
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Correlated spectral function (with real frequency self energy)
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--------------------------------------------------------------
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To produce both the momentum-integrated (total density of states or DOS) and orbitally-resolved (partial/projected DOS) spectral functions
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we can execute::
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SK.dos_parproj_basis(broadening=0.0, with_Sigma=True, with_dc=True, save_to_file=True)
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The variable `broadening` is an additional Lorentzian broadening (default: `0.01 eV`) applied to the resulting spectra.
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The output is written in the same way as described above for the :ref:`Wannier density of states <dos_wannier>`, but with filenames
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`DOS_parproj_*` instead.
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Momentum resolved spectral function (with real frequency self energy)
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---------------------------------------------------------------------
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Another quantity of interest is the momentum-resolved spectral function, which can directly be compared to ARPES
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experiments. First we have to execute `lapw1`, `lapw2 -almd` and :program:`dmftproj` with the `-band`
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option and use the :meth:`convert_bands_input <pytriqs.applications.dft.converters.wien2k_converter.Wien2kConverter.convert_bands_input>`
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routine, which converts the required files (for a more detailed description see :ref:`conversion`). The spectral function is then calculated by typing::
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SK.spaghettis(broadening=0.01,plot_shift=0.0,plot_range=None,ishell=None,save_to_file='Akw_')
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Here, optional parameters are
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* `shift`: An additional shift added as `(ik-1)*shift`, where `ik` is the index of the `k` point. This is useful for plotting purposes.
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The default value is 0.0.
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* `plotrange`: A list with two entries, :math:`\omega_{min}` and :math:`\omega_{max}`, which set the plot
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range for the output. The default value is `None`, in which case the full momentum range as given in the self energy is used.
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* `ishell`: An integer denoting the orbital index `ishell` onto which the spectral function is projected. The resulting function is saved in
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the files. The default value is `None`. Note for experts: The spectra are not rotated to the local coordinate system used in :program:`Wien2k`.
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The output is written as the 3-column files ``Akw(sp).dat``, where `(sp)` is defined as above. The output format is
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`k`, :math:`\omega`, `value`.
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