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Guard association term against FFT ringing artefacts #398

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Merged
prehner merged 1 commit into from
Oct 23, 2026
Merged

Guard association term against FFT ringing artefacts #398

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7 changes: 5 additions & 2 deletions crates/feos/src/pcsaft/dft/pure_saft_functional.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -123,10 +123,13 @@ impl<'a> FunctionalContribution for PureFMTAssocFunctional<'a> {
xi.iter_mut().zip(&n2).for_each(|(xi, &n2)| {
if n2.re() < N0_CUTOFF * 4.0 * PI * p.m[0] * r.re().powi(2) {
*xi = N::one();
} else if xi.re() < 0.0 {
*xi = N::zero(); // |n2v| > n2 only from FFT ringing; continuum bound xi in [0, 1]
}
});
let rho0 = (&n0 / p.m[0] * &xi).insert_axis(Axis(0));

// n0 < 0 only from FFT ringing; the association term needs rho0 >= 0 (sqrt(1 + 4 Delta rho0))
let n0p = n0.mapv(|n0| if n0.re() < 0.0 { N::zero() } else { n0 });
let rho0 = (&n0p / p.m[0] * &xi).insert_axis(Axis(0));
phi += &(a._helmholtz_energy_density(temperature, &rho0, &n2, &n3m1rec, &xi))?;
}

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