LMAXFOCK

LMAXFOCK = [integer]
Default: LMAXFOCK = 4 

Description: LMAXFOCK sets the maximum angular momentum quantum number l for the augmentation of charge densities in Hartree-Fock type routines.

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In the PAW method, the difference between the charge density of the all-electron partial waves and the pseudo partial waves $Q_{\alpha \beta }(r)=\phi _{\alpha }^{*}(r)\phi _{\beta }(r)-{\tilde {\phi }}_{\alpha }^{*}(r){\tilde {\phi }}_{\beta }(r)$ is usually restored on spherical grids centered at each atom (one-center terms inside the PAW spheres). To describe long range electrostatic effect, the moments of the differences of the all-electron and pseudo charge density also need to added on the plane wave grid. This is done up to a certain l quantum number. These augmentation charges restore the moments of the all-electron density on the plane wave grid. For the charge density, this augmentation is done exactly up to the maximum l quantum number required for the POTCAR files, whereas for the Fock exchange, the augmentation is controlled by LMAXFOCK.

Specifically, the exchange potential is given by $V_{\mathrm {x} }\left(\mathbf {r} ,\mathbf {r} '\right)=-{\frac {e^{2}}{2}}\sum _{\mathbf {q} m}f_{\mathbf {q} m}e^{-i\mathbf {q} \cdot \mathbf {r} '}{\frac {u_{\mathbf {q} m}^{*}(\mathbf {r} ')u_{\mathbf {q} m}(\mathbf {r} )}{\vert \mathbf {r} -\mathbf {r} '\vert }}e^{i\mathbf {q} \cdot \mathbf {r} }$ When the densit

This flag determines the treatment on the plane wave grid for the exact exchange. To compensate resulting errors, the contributions from the one-center terms are evaluated for the pseudo orbitals also only up to l=LMAXFOCK, whereas the one-center terms for the exact all-electron orbitals are evaluated up to the maximum required l (twice the angular quantum number of the partial wave with the highest l). The default is LMAXFOCK=4, and it might be required to increase this parameter, if the system contains f-electrons. Since this increases the computational load considerably (factor 2), it is recommended to perform tests, whether the results are already reasonably converged using the default LMAXFOCK=4.

To be compatible w.r.t. old releases, VASP also reads the flag HFLMAX to the same effect as LMAXFOCK.

Related Tags and Sections

HFLMAX, LMAXFOCKAE

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