From 78b74c8895a9aa555350da779b9efa28519c5a3b Mon Sep 17 00:00:00 2001
From: Bruno Ploumhans <13494793+Technici4n@users.noreply.github.com>
Date: Fri, 7 Feb 2025 20:18:37 +0100
Subject: [PATCH] Use DifferentationInterface instead of DiffResults (#1057)

---
 Project.toml              |  4 ++--
 src/postprocess/refine.jl | 15 ++++++---------
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/Project.toml b/Project.toml
index c073751120..17888ffb53 100644
--- a/Project.toml
+++ b/Project.toml
@@ -11,7 +11,7 @@ AtomsCalculators = "a3e0e189-c65a-42c1-833c-339540406eb1"
 Brillouin = "23470ee3-d0df-4052-8b1a-8cbd6363e7f0"
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 DftFunctionals = "6bd331d2-b28d-4fd3-880e-1a1c7f37947f"
-DiffResults = "163ba53b-c6d8-5494-b064-1a9d43ac40c5"
+DifferentiationInterface = "a0c0ee7d-e4b9-4e03-894e-1c5f64a51d63"
 DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
 FFTW = "7a1cc6ca-52ef-59f5-83cd-3a7055c09341"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
@@ -86,7 +86,7 @@ CUDA = "5"
 ComponentArrays = "0.15"
 Dates = "1"
 DftFunctionals = "0.3"
-DiffResults = "1.1"
+DifferentiationInterface = "0.6.39"
 DocStringExtensions = "0.9"
 DoubleFloats = "1"
 FFTW = "1.5"
diff --git a/src/postprocess/refine.jl b/src/postprocess/refine.jl
index 10c6867c20..7f35f6399c 100644
--- a/src/postprocess/refine.jl
+++ b/src/postprocess/refine.jl
@@ -34,7 +34,7 @@
 #     *Practical error bounds for properties in plane-wave electronic structure calculations*
 #     [SIAM Journal on Scientific Computing 44 (5), B1312-B1340](https://doi.org/10.1137/21M1456224)
 
-using DiffResults
+import DifferentiationInterface: AutoForwardDiff, value_and_derivative
 
 """
 Invert the metric operator M.
@@ -172,14 +172,13 @@ The refined energies can be obtained by E + dE.
 """
 function refine_energies(refinement::RefinementResult{T}) where {T}
     term_names = [string(nameof(typeof(term))) for term in refinement.basis.model.term_types]
-    result = DiffResults.DiffResult(zeros(T, length(term_names)),
-                                    zeros(T, length(term_names)))
+
     f(ε) = energy(refinement.basis,
                   refinement.ψ + ε.*refinement.δψ,
                   refinement.occupation;
                   ρ=refinement.ρ + ε.*refinement.δρ).energies.values
-    result = ForwardDiff.derivative!(result, f, zero(T))
-    (; E=Energies(term_names, result.value), dE=Energies(term_names, result.derivs[1]))
+    E, dE = value_and_derivative(f, AutoForwardDiff(), zero(T))
+    (; E=Energies(term_names, E), dE=Energies(term_names, dE))
 end
 
 """
@@ -193,13 +192,11 @@ function refine_forces(refinement::RefinementResult{T}) where {T}
     pack(x) = reinterpret(eltype(eltype(x)), x) # eltype is a Dual not just T!
     unpack(x) = reinterpret(SVector{3, T}, x)
 
-    result = DiffResults.DiffResult(zeros(T, 3*length(refinement.basis.model.positions)),
-                                    zeros(T, 3*length(refinement.basis.model.positions)))
     f(ε) = pack(compute_forces(refinement.basis,
                                refinement.ψ .+ ε.*refinement.δψ,
                                refinement.occupation;
                                ρ=refinement.ρ + ε.*refinement.δρ))
-    result = ForwardDiff.derivative!(result, f, zero(T))
+    F, dF = value_and_derivative(f, AutoForwardDiff(), zero(T))
 
-    (; F=unpack(result.value), dF=unpack(result.derivs[1]))
+    (; F=unpack(F), dF=unpack(dF))
 end