We will perform DFT+DMFT calcluations for the charge-transfer insulator NiO. We start from scratch and provide all necessary input files to do the calculations: First for doing a single-shot calculation.
states. In `[Group 1]` we define a group of two shells which are orthonormalized with
respect to states in an energy window from `-9` to `2` for all ions simultanously
(`NORMION = False`). We define the two shells, which correspond to the Ni d states
and the O p states. Only the Ni shell is treated as correlated (`CORR = True`), i.e.,
is supplemented with a Coulomb interaction later in the DMFT calculation.
Converting to hdf5 file
-------------------------------
We gather the output generated by :program:`plovasp` into a hdf5 archive which :program:`dft_tools` is able to read. We do this by running :program:`python converter.py` on the script :ref:`converter.py`:
Since the python script for performing the dmft loop pretty much resembles that presented in the tutorial on :ref:`SrVO3 <srvo3>`, we will not go into detail here but simply provide the script :ref:`nio.py`. Following Kunes et al. in `PRB 75 165115 (2007) <https://journals.aps.org/prb/abstract/10.1103/PhysRevB.75.165115>`_ we use :math:`U=8` and :math:`J=1`. We select :math:`\beta=5` instead of :math:`\beta=10` to ease the problem slightly. For simplicity we fix the double-counting potential to :math:`\mu_{DC}=59` eV by::
For sensible results run this script in parallel on at least 20 cores. As a quick check of the results, we can compare the orbital occupation from the paper cited above (:math:`n_{eg} = 0.54` and :math:`n_{t2g}=1.0`) and those from the cthyb output (check lines `Orbital up_0 density:` for a t2g and `Orbital up_2 density:` for an eg orbital). They should coincide well.
We calculate the local lattice Green's function - now also for the uncorrelated orbitals, i.e., the O p states, for what we use the script :ref:`NiO_local_lattice_GF.py`. The result is saved in the h5 file as `G_latt_orb_it<n_it>`, where `<n_it>` is the number of the last DMFT iteration.
To compare to results from literature we make use of the `maxent triqs application <https://triqs.github.io/maxent/master/>`_ and calculate the spectral function on real axis. Use this script to perform a crude but quick calculation: :ref:`maxent.py` using a linear real axis and a line-fit analyzer to determine the optimal :math:`\alpha`. The output is saved in the h5 file in `DMFT_results/Iterations/G_latt_orb_w_o<n_o>_it<n_it>`, where `<n_o>` is the number of the orbital and `n_it` is again the number of the last iteration. The real axis information is stored in `DMFT_results/Iterations/w_it<n_it>`.
In this part we will perform charge self-consistent DMFT calculations. To do so we have to adapt the VASP `INCAR` such that :program:`VASP` reads the updated charge density after each step. We add the lines::
which makes VASP wait after each step of its iterative diagonalization until the file vasp.lock is created. It then reads the update of the charge density in the file `GAMMA`. It is terminated by an external script after a desired amount of steps, such that we deactivate all automatic stoping criterion by setting the number of steps to a very high number.
We take the respective converged DFT and DMFT calculations from before as a starting point. I.e., we copy the `CHGCAR` and `nio.h5` together with the other :program:`VASP` input files and :file:`plo.cfg` in a new directory. We use a script called :program:`vasp_dmft` to invoke :program:`VASP` in the background and start the DMFT calculation together with :program:`plovasp` and the converter. This script assumes that the dmft sript contains a function `dmft_cycle()` and also the conversion from text files to the h5 file. Additionally we have to add a few lines to calculate the density correction and calculate the correlation energy. We adapt the script straightforardly (for a working example see :ref:`nio_csc.py`). The most important new lines are::
where the chemical potential is determined to a greater precision than before, the correction to the dft density matrix is calculated and output to the file :file:`GAMMA`. The correlation energy is calculated via Migdal-Galitzki formula. We also slightly increase the tolerance for the detection of blocks since the DFT calculation now includes some QMC noise.
