Implementation of DFT+U

.github/workflows/makefile.yml

@@ -148,6 +148,12 @@ jobs:
         mpirun -np ${{matrix.np}} ../../bin/Conquest
         cat Conquest_out
 
+    - name: Run test 009
+      working-directory: ${{github.workspace}}/testsuite/test_009_DFT_plus_U
+      run: |
+        mpirun -np ${{matrix.np}} ../../bin/Conquest
+        cat Conquest_out
+
     - name: Check test results
       working-directory: ${{github.workspace}}/testsuite
       run: pytest test_check_output.py

docs/groundstate.rst

@@ -393,6 +393,38 @@ cell (or some important length scale in your system).
 
 Go to :ref:`top <groundstate>`.
 
+.. _gs_func_hubbard_U:
+
+Hubbard U and XC Functionals
+----------------------------
+
+CONQUEST now supports the DFT+U formalism, as described by :cite:`g-Cococcioni:2005aa`.
+The relevant input tags are:
+
+::
+
+   DM.DFTplusU T
+   DM.WriteOccMat T (default)
+
+   # Species, n, l, zeta, U (Ha)
+   %block DFTplusU
+   1 3 2 1 0.0772
+   %endblock
+
+The ``DFTplusU`` block specifies the projectors onto the correlated subspace (at present
+these must be PAOs) and requires one line per species.  The block specifies n, l, zeta
+and the value of U (in Hartrees).  We strongly recommend that PAOs created with
+equal energies are used (in the PAO generation, add ``Atom.Cutoffs energy`` to the
+atom block), and that the largest radius zeta function (i.e. zeta=1) is used.  Careful
+testing is needed for the projectors and an appropriate value of U (we note that when using
+the same pseudopotentials, CONQUEST and QuantumEspresso calculations agree very well).
+
+The exchange-correlation (XC) functional is (almost always) set by the ion files
+used to specify the elements (and generated by the :ref:`PAO generation <generating_paos>` tool).
+It is possible to run a calculation using a different XC functional to the ion
+files by setting ``General.DifferentFunctional T`` and ``General.FunctionalType <integer>`` which
+is documented in the :ref:`General <input_general>` section of the input tags documentation.
+
 .. _gs_suppfunc:
 
 Support functions

docs/references.bib

@@ -708,4 +708,18 @@ @article{Neugebauer1992
   pages = {16067--16080},
   year = {1992},
   doi = {10.1103/PhysRevB.46.16067}
+}
+@article{Cococcioni:2005aa,
+  title = {Linear response approach to the calculation of the effective interaction parameters in the $\mathrm{LDA}+\mathrm{U}$ method},
+  author = {Cococcioni, Matteo and de Gironcoli, Stefano},
+  journal = {Phys. Rev. B},
+  volume = {71},
+  issue = {3},
+  pages = {035105},
+  numpages = {16},
+  year = {2005},
+  month = {Jan},
+  publisher = {American Physical Society},
+  doi = {10.1103/PhysRevB.71.035105},
+  url = {https://link.aps.org/doi/10.1103/PhysRevB.71.035105}
 }