ESF SPLINES

ESF_SPLINES = .FALSE. | .TRUE.
Default: ESF_SPLINES = .FALSE. 

Description: ESF_SPLINES selects k-point interpolation in ACFDT(R) calculations using tri-cubic splines.

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Interpolates the electronic structure factor in ACFDT/RPA calculations using tri-cubic splines to accelerate k-point convergence of the RPA correlation energy. This feature follows the same idea as in coupled cluster calculations.

To this end, the electronic structure factor in the RPA

$S(\mathbf{𝐪}+\mathbf{𝐆})=\int \mathrm{d}\omega \{(\mathrm{l}\mathrm{n}[1-{\tilde{\chi }}^0(\mathbf{𝐪},\mathrm{i}\omega )V(\mathbf{𝐪})]{)}_{\mathbf{𝐆},\mathbf{𝐆}}+V_{\mathbf{𝐆},\mathbf{𝐆}}(\mathbf{𝐪}){\tilde{\chi }}^0(\mathbf{𝐪},\mathrm{i}\omega )\}$

is evaluated on the k-point grid defined in KPOINTS and the correlation energy (as its trace) is stored. To obtain the correlation energy on a finer k-point grid, more q-points are added using tri-cubic spline interpolation and the resulting energy is compared to the previous correlation energy. This procedure is repeated ESF_NINTER times until the difference in energy between the interpolation steps is less than ESF_CONV. The default settings of ESF_NINTER and ESF_CONV typically yield similar k-point convergence compared to the k-p perturbation theory approach, where the limit $\underset{\mathbf{𝐪}\mathbf{\to }\mathbf{𝟎}}{\lim }{\tilde{\chi }}_{{\mathbf{𝐆}\mathbf{𝐆}}^{\prime }}^0(\mathbf{𝐪},\mathrm{i}\omega )\cdot {\mathbf{𝐕}}_{\mathbf{𝐆}{\mathbf{𝐆}}^{\prime }}(\mathbf{𝐪})$ is stored to WAVECAR in a preceding DFT calculation using LOPTICS=T.

Tip: This method works for metals and insulators.

Warning: Remove WAVEDER before running the job and avoid setting LOPTICS.

Related tags and articles

ESF_CONV, ESF_NINTER, LOPTICS

Examples that use this tag

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