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Interface

API documentation for DftFunctionals.

See in particular the key functions potential_terms and kernel_terms.

Missing documentation

More details on the public interface are needed.

DftFunctionals.DftFunctional — Method
DftFunctional(identifier::Symbol, args...; kwargs...)

A generic DFT functional implementation. Valid identifiers are the ones supported by Libxc as symbols, e.g. :lda_x, hyb_gga_xc_b3lyp. Only a subset of functionals is currently available. Additional arguments and kwargs are passed to the functional (e.g. to modify functional parameters).

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DftFunctionals.change_parameters — Method

Return a new version of the passed functional with its parameters adjusted. This may not be a copy in case no changes are done to its internal parameters. Generally the identifier of the functional will be changed to reflect the change in parameter values unless keep_identifier is true. To get the tuple of adjustable parameters and their current values check out parameters. It is not checked that the correct parameters are passed.

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DftFunctionals.family — Method

Return the family of a functional. Results are :lda, :gga, :mgga and :mggal (Meta-GGA requiring Laplacian of ρ)

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DftFunctionals.has_energy — Method

Does this functional support energy evaluations? Some don't, in which case energy terms will not be returned by potential_terms and kernel_terms, i.e. e will be false (a strong zero).

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DftFunctionals.kernel_terms — Function
kernel_terms(f::Functional, ρ, [σ, τ, Δρ])

Evaluate energy, potential and kernel terms at a real-space grid of densities, density derivatives etc. Not required derivatives for the functional type will be ignored. Returns a named tuple with the same keys as potential_terms and additionally second-derivative cross terms such as Vρσ ($\frac{∂^2e}{∂ρ∂σ}$).

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DftFunctionals.kind — Method

Return the functional kind: :x (exchange), :c (correlation), :k (kinetic) or :xc (exchange and correlation combined)

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DftFunctionals.potential_terms — Function
potential_terms(f::Functional, ρ, [σ, τ, Δρ])

Evaluate energy and potential terms at a real-space grid of densities, density derivatives etc. Not required derivatives for the functional type will be ignored. Returns a named tuple with keys e (Energy per unit volume), Vρ ($\frac{∂e}{∂ρ}$), Vσ ($\frac{∂e}{∂σ}$), Vτ ($\frac{∂e}{∂τ}$), Vl ($\frac{∂e}{∂(Δρ)}$).

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DftFunctionals.spinindex_σ — Method

In the functional interface we explicitly use the symmetry $σ_{αβ} = σ_{βα}$ for the contracted density gradient $σ_ij = ∇ρ_i ⋅ ∇ρ_j$ where $i,j ∈ \{α, β\}$. Instead of treating $σ$ to have the spin components $σ_{αα}$, $σ_{αβ}$, $σ_{βα}$ and $σ_{ββ}$, we consider it to have three pseudo-spin components $σ_{αα}$, $σ_x$ and $σ_{ββ}$, where $σ_x = (σ_{αβ} + σ_{βα})/2 = σ_{αβ}$. Input arrays like σ or output arrays like Vσ or Vρσ will therefore feature a spin axis of length 3 refering to the $σ_{αα}$, $σ_{αβ}$ and $σ_{ββ}$ components / derivatives respectively. E.g. σ is of shape (3, n_p) (where n_p is the number of points where evaluation takes place.

This function maps the "unfolded" spin tuple (i, j) in $σ_ij$ to the corresponding place in the length-3 spin axis of σ.

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