Struct D4Model 

pub struct D4Model {
    pub nat: usize,
    pub elements: Vec<u8>,
    pub cn: Vec<f64>,
    /* private fields */
}

Pre-computed self-consistent D4 model.

Created once before the SCC loop, holds the dispersion matrix and coordination numbers. At each SCC iteration, call weight_references with current charges, then get_potential and get_energy.

Fields

nat: usize

elements: Vec<u8>

cn: Vec<f64>

D4 coordination numbers (electronegativity-weighted, DFT-D3 type).

Implementations

impl D4Model

pub fn new(elements: &[u8], positions: &[[f64; 3]]) -> Self

Create a new D4 model for the given molecular geometry.

Computes D4 coordination numbers, scaled reference polarizabilities, reference C6 coefficients, and the BJ-damped dispersion matrix.

pub fn weight_references(&self, charges: &[f64]) -> D4Weights

Compute reference weights from coordination numbers and charges.

This implements weight_references from dftd4, computing gwvec and dgwdq for each atom and reference using CN-dependent Gaussian weighting with charge-dependent zeta scaling.

pub fn get_potential(&self, weights: &D4Weights) -> Vec<f64>

Compute the D4 atom-resolved potential for the Fock matrix.

Returns vat[iat] to be added to pot%vat (atom-resolved charge potential). Formula: vat[iat] = Σ_iref Σ_jat Σ_jref dispmat[iref,iat,jref,jat] * dgwdq[iat][iref] * gwvec[jat][jref]

This is the ncoup=1 (atom-wise weighting) path from tblite.

pub fn get_energy(&self, weights: &D4Weights) -> f64

Compute the self-consistent D4 pairwise dispersion energy.

E_disp = 0.5 * Σ_iat Σ_iref Σ_jat Σ_jref gwvec[iat][iref] * dispmat * gwvec[jat][jref]

pub fn get_atm_energy(&self, positions: &[[f64; 3]]) -> f64

Compute ATM three-body dispersion energy (non-SC, uses q=0 weights).

This is the get_engrad / get_dispersion3 path from tblite, evaluated with zero charges.