.. _conversion: Orbital construction and conversion =================================== The first step for a DMFT calculation is to provide the necessary input based on a DFT calculation. We will not review how to do the DFT calculation here in this documentation, but refer the user to the documentation and tutorials that come with the actual DFT package. Here, we will describe how to use output created by Wien2k, as well as how to use the light-weight general interface. Interface with Wien2k --------------------- We assume that the user has obtained a self-consistent solution of the Kohn-Sham equations. We further have to require that the user is familiar with the main in/output files of Wien2k, and how to run the DFT code. Conversion for the DMFT self-consistency cycle """""""""""""""""""""""""""""""""""""""""""""" First, we have to write the necessary quantities into a file that can be processed further by invoking in a shell the command `x lapw2 -almd` We note that any other flag for lapw2, such as -c or -so (for spin-orbit coupling) has to be added also to this line. This creates some files that we need for the Wannier orbital construction. The orbital construction itself is done by the Fortran program :program:`dmftproj`. For an extensive manual to this program see :download:`TutorialDmftproj.pdf `. Here we will only describe the basic steps. Let us take the compound SrVO3, a commonly used example for DFT+DMFT calculations. The input file for :program:`dmftproj` looks like .. literalinclude:: images_scripts/SrVO3.indmftpr The first three lines give the number of inequivalent sites, their multiplicity (to be in accordance with the Wien2k *struct* file) and the maximum orbital quantum number :math:`l_{max}`. In our case our struct file contains the atoms in the order Sr, V, O. Next we have to specify for each of the inequivalent sites, whether we want to treat their orbitals as correlated or not. This information is given by the following 3 to 5 lines: #. We specify which basis set is used (complex or cubic harmonics). #. The four numbers refer to *s*, *p*, *d*, and *f* electrons, resp. Putting 0 means doing nothing, putting 1 will calculate **unnormalized** projectors in compliance with the Wien2k definition. The important flag is 2, this means to include these electrons as correlated electrons, and calculate normalized Wannier functions for them. In the example above, you see that only for the vanadium *d* we set the flag to 2. If you want to do simply a DMFT calculation, then set everything to 0, except one flag 2 for the correlated electrons. #. In case you have a irrep splitting of the correlated shell, you can specify here how many irreps you have. You see that we put 2, since eg and t2g symmetries are irreps in this cubic case. If you don't want to use this splitting, just put 0. #. (optional) If you specifies a number different from 0 in above line, you have to tell now, which of the irreps you want to be treated correlated. We want to t2g, and not the eg, so we set 0 for eg and 1 for t2g. Note that the example above is what you need in 99% of the cases when you want to treat only t2g electrons. For eg's only (e.g. nickelates), you set 10 and 01 in this line. #. (optional) If you have specified a correlated shell for this atom, you have to tell if spin-orbit coupling should be taken into account. 0 means no, 1 is yes. These lines have to be repeated for each inequivalent atom. The last line gives the energy window, relative to the Fermi energy, that is used for the projective Wannier functions. Note that, in accordance with Wien2k, we give energies in Rydberg units! After setting up this input file, you run: `dmftproj` Again, adding possible flags like -so for spin-orbit coupling. This program produces the following files (in the following, take *case* as the standard Wien2k place holder, to be replaced by the actual working directory name): * :file:`case.ctqmcout` and :file:`case.symqmc` containing projector operators and symmetry operations for orthonormalized Wannier orbitals, respectively. * :file:`case.parproj` and :file:`case.sympar` containing projector operators and symmetry operations for uncorrelated states, respectively. These files are needed for projected density-of-states or spectral-function calculations in post-processing only. * :file:`case.oubwin` needed for the charge density recalculation in the case of fully self-consistent DFT+DMFT run (see below). Now we convert these files into an hdf5 file that can be used for the DMFT calculations. For this purpose we use the python module :class:`Wien2kConverter `. It is initialized as:: from triqs_dft_tools.converters.wien2k_converter import * Converter = Wien2kConverter(filename = case) The only necessary parameter to this construction is the parameter `filename`. It has to be the root of the files produces by dmftproj. For our example, the :program:`Wien2k` naming convention is that all files are called the same, for instance :file:`SrVO3.*`, so you would give `filename = "SrVO3"`. The constructor opens an hdf5 archive, named :file:`case.h5`, where all the data is stored. For other parameters of the constructor please visit the :ref:`refconverters` section of the reference manual. After initializing the interface module, we can now convert the input text files to the hdf5 archive by:: Converter.convert_dft_input() This reads all the data, and stores it in the file :file:`case.h5`. In this step, the files :file:`case.ctqmcout` and :file:`case.symqmc` have to be present in the working directory. After this step, all the necessary information for the DMFT loop is stored in the hdf5 archive, where the string variable `Converter.hdf_filename` gives the file name of the archive. At this point you should use the method :meth:`dos_wannier_basis ` contained in the module :class:`SumkDFTTools ` to check the density of states of the Wannier orbitals (see :ref:`analysis`). You have now everything for performing a DMFT calculation, and you can proceed with the section on :ref:`single-shot DFT+DMFT calculations `. Data for post-processing """""""""""""""""""""""" In case you want to do post-processing of your data using the module :class:`SumkDFTTools `, some more files have to be converted to the hdf5 archive. For instance, for calculating the partial density of states or partial charges consistent with the definition of :program:`Wien2k`, you have to invoke:: Converter.convert_parproj_input() This reads and converts the files :file:`case.parproj` and :file:`case.sympar`. If you want to plot band structures, one has to do the following. First, one has to do the Wien2k calculation on the given :math:`\mathbf{k}`-path, and run :program:`dmftproj` on that path: | `x lapw1 -band` | `x lapw2 -band -almd` | `dmftproj -band` Again, maybe with the optional additional extra flags according to Wien2k. Now we use a routine of the converter module allows to read and convert the input for :class:`SumkDFTTools `:: Converter.convert_bands_input() After having converted this input, you can further proceed with the :ref:`analysis`. For more options on the converter module, please have a look at the :ref:`refconverters` section of the reference manual. Data for transport calculations """"""""""""""""""""""""""""""" For the transport calculations, the situation is a bit more involved, since we need also the :program:`optics` package of Wien2k. Please look at the section on :ref:`Transport` to see how to do the necessary steps, including the conversion. Interface with VASP --------------------- .. warning:: The VASP interface is in the alpha-version and the VASP part of it is not yet publicly released. The documentation may, thus, be subject to changes before the final release. Note that this VASP interface relies on new options introduced since version 5.4.x. Additionally, the interface only works correctly if the k-point symmetries are turned off during the VASP run (ISYM=-1). The output of raw (non-normalized) projectors is controlled by an INCAR option LOCPROJ whose complete syntax is described in the VASP documentaion. The definition of a projector set starts with specifying which sites and which local states we are going to project onto. This information is provided by option LOCPROJ | `LOCPROJ = : : ` where `` represents a list of site indices separated by spaces, with the indices corresponding to the site position in the POSCAR file; `` specifies local states (e.g. :math:`s`, :math:`p`, :math:`d`, :math:`d_{x^2-y^2}`, etc.); `` chooses a particular type of the local basis function. Some projector types also require parameters `EMIN`, `EMAX` in INCAR to be set to define an (approximate) energy window corresponding to the valence states. When either a self-consistent (`ICHARG < 10`) or a non-self-consistent (`ICHARG >= 10`) calculation is done VASP produces file `LOCPROJ` which will serve as the main input for the conversion routine. Conversion for the DMFT self-consistency cycle """""""""""""""""""""""""""""""""""""""""""""" In order to use the projectors generated by VASP for defining an impurity problem they must be processed, i.e. normalized, possibly transformed, and then converted to a format suitable for DFT_tools scripts. Currently, it is necessary to add the Fermi energy by hand as the fifth value in the first line of the LOCPROJ file before the next steps can be executed. The processing of projectors is performed by the program :program:`plovasp` invoked as | `plovasp ` where `` is a input file controlling the conversion of projectors. The format of input file `` is described in details in :ref:`plovasp`. Here we just give a simple example for the case of SrVO3: .. literalinclude:: images_scripts/srvo3.cfg A projector shell is defined by a section `[Shell 1]` where the number can be arbitrary and used only for user convenience. Several parameters are required - **IONS**: list of site indices which must be a subset of indices given earlier in `LOCPROJ`. - **LSHELL**: :math:`l`-quantum number of the projector shell; the corresponding orbitals must be present in `LOCPROJ`. - **EWINDOW**: energy window in which the projectors are normalized; note that the energies are defined with respect to the Fermi level. Option **TRANSFORM** is optional but here it is specified to extract only three :math:`t_{2g}` orbitals out of five `d` orbitals given by :math:`l = 2`. For the conversion to a h5 file we use on the python level (in analogy to the Wien2kConverter):: from triqs_dft_tools.converters.vasp_converter import * Converter = VaspConverter(filename = filename) Converter.convert_dft_input() As usual, the resulting h5-file can then be used with the SumkDFT class. Note that the automatic detection of the correct blockstructure might fail for VASP inputs. This can be circumvented by increase the :class:`SumkDFT ` threshold to e.g.:: SK.analyse_block_structure(threshold = 1e-4) However, only do this after a careful study of the density matrix and the dos in the wannier basis. A general H(k) -------------- In addition to the more complicated Wien2k converter, :program:`DFTTools` contains also a light converter. It takes only one inputfile, and creates the necessary hdf outputfile for the DMFT calculation. The header of this input file has a defined format, an example is the following (do not use the text/comments in your input file): .. literalinclude:: images_scripts/case.hk The lines of this header define #. Number of :math:`\mathbf{k}`-points used in the calculation #. Electron density for setting the chemical potential #. Number of total atomic shells in the hamiltonian matrix. In short, this gives the number of lines described in the following. IN the example file give above this number is 2. #. The next line(s) contain four numbers each: index of the atom, index of the equivalent shell, :math:`l` quantum number, dimension of this shell. Repeat this line for each atomic shell, the number of the shells is given in the previous line. In the example input file given above, we have two inequivalent atomic shells, one on atom number 1 with a full d-shell (dimension 5), and one on atom number 2 with one p-shell (dimension 3). Other examples for these lines are: #. Full d-shell in a material with only one correlated atom in the unit cell (e.g. SrVO3). One line is sufficient and the numbers are `1 1 2 5`. #. Full d-shell in a material with two equivalent atoms in the unit cell (e.g. FeSe): You need two lines, one for each equivalent atom. First line is `1 1 2 5`, and the second line is `2 1 2 5`. The only difference is the first number, which tells on which atom the shell is located. The second number is the same in both lines, meaning that both atoms are equivalent. #. t2g orbitals on two non-equivalent atoms in the unit cell: Two lines again. First line is `1 1 2 3`, second line `2 2 2 3`. The difference to the case above is that now also the second number differs. Therefore, the two shells are treated independently in the calculation. #. d-p Hamiltonian in a system with two equivalent atoms each in the unit cell (e.g. FeSe has two Fe and two Se in the unit cell). You need for lines. First line `1 1 2 5`, second line `2 1 2 5`. These two lines specify Fe as in the case above. For the p orbitals you need line three as `3 2 1 3` and line four as `4 2 1 3`. We have 4 atoms, since the first number runs from 1 to 4, but only two inequivalent atoms, since the second number runs only form 1 to 2. Note that the total dimension of the hamiltonian matrices that are read in is the sum of all shell dimensions that you specified. For example number 4 given above we have a dimension of 5+5+3+3=16. It is important that the order of the shells that you give here must be the same as the order of the orbitals in the hamiltonian matrix. In the last example case above the code assumes that matrix index 1 to 5 belongs to the first d shell, 6 to 10 to the second, 11 to 13 to the first p shell, and 14 to 16 the second p shell. #. Number of correlated shells in the hamiltonian matrix, in the same spirit as line 3. #. The next line(s) contain six numbers: index of the atom, index of the equivalent shell, :math:`l` quantum number, dimension of the correlated shells, a spin-orbit parameter, and another parameter defining interactions. Note that the latter two parameters are not used at the moment in the code, and only kept for compatibility reasons. In our example file we use only the d-shell as correlated, that is why we have only one line here. #. The last line contains several numbers: the number of irreducible representations, and then the dimensions of the irreps. One possibility is as the example above, another one would be 2 2 3. This would mean, 2 irreps (eg and t2g), of dimension 2 and 3, resp. After these header lines, the file has to contain the Hamiltonian matrix in orbital space. The standard convention is that you give for each :math:`\mathbf{k}`-point first the matrix of the real part, then the matrix of the imaginary part, and then move on to the next :math:`\mathbf{k}`-point. The converter itself is used as:: from triqs_dft_tools.converters.hk_converter import * Converter = HkConverter(filename = hkinputfile) Converter.convert_dft_input() where :file:`hkinputfile` is the name of the input file described above. This produces the hdf file that you need for a DMFT calculation. For more options of this converter, have a look at the :ref:`refconverters` section of the reference manual. Wannier90 Converter ------------------- Using this converter it is possible to convert the output of `wannier90 `_ Maximally Localized Wannier Functions (MLWF) and create a HDF5 archive suitable for one-shot DMFT calculations with the :class:`SumkDFT ` class. The user must supply two files in order to run the Wannier90 Converter: #. The file :file:`seedname_hr.dat`, which contains the DFT Hamiltonian in the MLWF basis calculated through :program:`wannier90` with ``hr_plot = true`` (please refer to the :program:`wannier90` documentation). #. A file named :file:`seedname.inp`, which contains the required information about the :math:`\mathbf{k}`-point mesh, the electron density, the correlated shell structure, ... (see below). Here and in the following, the keyword ``seedname`` should always be intended as a placeholder for the actual prefix chosen by the user when creating the input for :program:`wannier90`. Once these two files are available, one can use the converter as follows:: from triqs_dft_tools.converters import Wannier90Converter Converter = Wannier90Converter(seedname='seedname') Converter.convert_dft_input() The converter input :file:`seedname.inp` is a simple text file with the following format (do not use the text/comments in your input file): .. literalinclude:: images_scripts/LaVO3_w90.inp The example shows the input for the perovskite crystal of LaVO\ :sub:`3` in the room-temperature `Pnma` symmetry. The unit cell contains four symmetry-equivalent correlated sites (the V atoms) and the total number of electrons per unit cell is 8 (see second line). The first line specifies how to generate the :math:`\mathbf{k}`-point mesh that will be used to obtain :math:`H(\mathbf{k})` by Fourier transforming :math:`H(\mathbf{R})`. Currently implemented options are: * :math:`\Gamma`-centered uniform grid with dimensions :math:`n_{k_x} \times n_{k_y} \times n_{k_z}`; specify ``0`` followed by the three grid dimensions, like in the example above * :math:`\Gamma`-centered uniform grid with dimensions automatically determined by the converter (from the number of :math:`\mathbf{R}` vectors found in :file:`seedname_hr.dat`); just specify ``-1`` Inside :file:`seedname.inp`, it is crucial to correctly specify the correlated shell structure, which depends on the contents of the :program:`wannier90` output :file:`seedname_hr.dat` and on the order of the MLWFs contained in it. In this example we have four lines for the four V atoms. The MLWFs were constructed for the t\ :sub:`2g` subspace, and thus we set ``l`` to 2 and ``dim`` to 3 for all V atoms. Further the spin-orbit coupling (``SO``) is set to 0 and ``irep`` to 0. As in this example all 4 V atoms are equivalent we set ``sort`` to 0. We note that, e.g., for a magnetic DMFT calculation the correlated atoms can be made inequivalent at this point by using different values for ``sort``. The number of MLWFs must be equal to, or greater than the total number of correlated orbitals (i.e., the sum of all ``dim`` in :file:`seedname.inp`). If the converter finds fewer MLWFs inside :file:`seedname_hr.dat`, then it stops with an error; if it finds more MLWFs, then it assumes that the additional MLWFs correspond to uncorrelated orbitals (e.g., the O-\ `2p` shells). When reading the hoppings :math:`\langle w_i | H(\mathbf{R}) | w_j \rangle` (where :math:`w_i` is the :math:`i`-th MLWF), the converter also assumes that the first indices correspond to the correlated shells (in our example, the V-t\ :sub:`2g` shells). Therefore, the MLWFs corresponding to the uncorrelated shells (if present) must be listed **after** those of the correlated shells. With the :program:`wannier90` code, this can be achieved by listing the projections for the uncorrelated shells after those for the correlated shells. In our `Pnma`-LaVO\ :sub:`3` example, for instance, we could use:: Begin Projections V:l=2,mr=2,3,5:z=0,0,1:x=-1,1,0 O:l=1:mr=1,2,3:z=0,0,1:x=-1,1,0 End Projections where the ``x=-1,1,0`` option indicates that the V--O bonds in the octahedra are rotated by (approximatively) 45 degrees with respect to the axes of the `Pbnm` cell. The converter will analyse the matrix elements of the local Hamiltonian to find the symmetry matrices `rot_mat` needed for the global-to-local transformation of the basis set for correlated orbitals (see section :ref:`hdfstructure`). The matrices are obtained by finding the unitary transformations that diagonalize :math:`\langle w_i | H_I(\mathbf{R}=0,0,0) | w_j \rangle`, where :math:`I` runs over the correlated shells and `i,j` belong to the same shell (more details elsewhere...). If two correlated shells are defined as equivalent in :file:`seedname.inp`, then the corresponding eigenvalues have to match within a threshold of 10\ :sup:`-5`, otherwise the converter will produce an error/warning. If this happens, please carefully check your data in :file:`seedname_hr.dat`. This method might fail in non-trivial cases (i.e., more than one correlated shell is present) when there are some degenerate eigenvalues: so far tests have not shown any issue, but one must be careful in those cases (the converter will print a warning message). The current implementation of the Wannier90 Converter has some limitations: * Since :program:`wannier90` does not make use of symmetries (symmetry-reduction of the :math:`\mathbf{k}`-point grid is not possible), the converter always sets ``symm_op=0`` (see the :ref:`hdfstructure` section). * No charge self-consistency possible at the moment. * Calculations with spin-orbit (``SO=1``) are not supported. * The spin-polarized case (``SP=1``) is not yet tested. * The post-processing routines in the module :class:`SumkDFTTools ` were not tested with this converter. * ``proj_mat_all`` are not used, so there are no projectors onto the uncorrelated orbitals for now. MPI issues ---------- The interface packages are written such that all the file operations are done only on the master node. In general, the philosophy of the package is that whenever you read in something from the archive yourself, you have to *manually* broadcast it to the nodes. An exception to this rule is when you use routines from :class:`SumkDFT ` or :class:`SumkDFTTools `, where the broadcasting is done for you. Interfaces to other packages ---------------------------- Because of the modular structure, it is straight forward to extend the :ref:`TRIQS ` package in order to work with other band-structure codes. The only necessary requirement is that the interface module produces an hdf5 archive, that stores all the data in the specified form. For the details of what data is stored in detail, see the :ref:`hdfstructure` part of the reference manual.