NATURALO

NATURALO = [integer]
Default: NATURALO = 0

Description: calculate RPA natural orbitals.

If ALGO = G0W0R or ALGO = GWR, the VASP code diagonalizes the RPA density matrix and writes the final natural orbitals to the WAVECAR file. The one-electron occupancies on the WAVECAR file are also updated to the eigevalues of the RPA density matrix.

The following settings are currently supported

NATURALO=0 calculates the density matrix, diagonalizes the matrix and writes the natural orbitals and eigenvalues of the density matrix to the file WAVECAR.

NATURALO=1 calculates the density matrix, diagonalizes the matrix only in the sub-block of unoccupied states, and writes the occupied Kohn Sham as well as natural orbitals corresponding to unoccupied states to the file WAVECAR. This should be only used for gapped systems (insulators and semiconductors). The one-electron occupancies are not updated (should remain 1 and 0).

NATURALO=negative value: Similar to NATURALO=1 but additionally conserve |NATURALO| unoccupied states. This is expedient, for subsequent GW calculations, to conserve few unoccupied orbitals to their Kohn-Sham state.

If 10 is added (e.g. NATURALO=10, NATURALO=12, NATURALO=11) the density matrix is diagonalizes using a perturbative Loewdin algorithm that attempts to keep the orbital order strictly conserved: E.g. orbital, the natural orbital matching closest the Nth Kohn-Sham orbital will be stored.

NATURALO=2 (or 12) is similar to 0, but the one-electron occupancies are not updated. In rare cases this might lead to inconsistencies, if the orbital order changes between DFT and the RPA density matrix (i.e. a previously occupied DFT orbitals posses a small occupation in the RPA density matrix and is moved into the unoccupied block). Use this with care and only for gapped systems. This flag in combination with ALGO = GWR, can be used to evaluate the GW-singles contribution to the correlation energy. One can deduct the singles energies from the energies after

Energies after update of density matrix
Hartree-Fock free energy of the ion-electron system (eV)

Experience has shown that there is very little difference between the orbitals obtained using ALGO = G0W0R and ALGO = GWR. We strongly recommend to use the more efficient and better tested algorithm ALGO = G0W0R. Furthermore, perform careful tests for NOMEGA: the RPA total energy converges much faster then the natural orbitals. Using a too small NOMEGA can yields natural orbitals that are non-optimal, leading to very slow convergence of correlated calculations with respect to the number of natural orbitals.

Related Tags and Sections

ALGO for response functions and RPA calculations
for an overview ACFDT/RPA calculations