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Implement UKS nuclear gradients for Laplacian-dependent meta-GGAs #229

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Implement UKS nuclear gradients for Laplacian-dependent meta-GGAs #229

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6afe6ff
Fix per-atom error in the Laplacian meta-GGA nuclear gradient
susilehtola Sep 15, 2026
3e035f8
Implement UKS nuclear gradients for Laplacian-dependent meta-GGAs
susilehtola Sep 15, 2026
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72 changes: 61 additions & 11 deletions src/xc_integrator/replicated/host/reference_replicated_xc_host_integrator_exc_grad.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -118,9 +118,6 @@ void ReferenceReplicatedXCHostIntegrator<ValueType>::

// MGGA constants
const bool needs_laplacian = func.needs_laplacian();
if(needs_laplacian and is_uks) {
GAUXC_GENERIC_EXCEPTION("UKS Gradients + Laplacian Dependent MGGAs is Not Yet Implemented");
}

// Misc KS settings
IntegratorSettingsEXC_GRAD exc_grad_settings;
Expand Down Expand Up @@ -203,6 +200,9 @@ void ReferenceReplicatedXCHostIntegrator<ValueType>::
host_data.tau .resize( spin_dim_scal * npts );
host_data.vtau.resize( spin_dim_scal * npts );
if ( needs_laplacian ) {
// One more block holds 2 P lapl(B), which the nuclear derivative
// of lapl(rho) contracts against; see the assembly below.
host_data.zmat .resize( 5 * spin_dim_scal * npts * nbe );
host_data.basis_eval.resize( 24 * npts * nbe ); // 11 + lapl_grad(3) + der3(10)
host_data.lapl .resize( spin_dim_scal * npts );
host_data.vlapl.resize( spin_dim_scal * npts );
Expand All @@ -222,6 +222,8 @@ void ReferenceReplicatedXCHostIntegrator<ValueType>::
double* xZmat_x = nullptr;
double* xZmat_y = nullptr;
double* xZmat_z = nullptr;
double* xLmat = nullptr; // fac P lapl(B), laplacian mGGAs only
double* xZLmat = nullptr;

auto* eps = host_data.eps.data();
auto* gamma = host_data.gamma.data();
Expand Down Expand Up @@ -358,6 +360,18 @@ void ReferenceReplicatedXCHostIntegrator<ValueType>::
blas::lacpy( 'A', nbe, npts, d3basis_xxz_eval, nbe, dlgradbasis_z_eval, nbe );
blas::axpy( nbe * npts, 1., d3basis_yyz_eval, 1, dlgradbasis_z_eval, 1);
blas::axpy( nbe * npts, 1., d3basis_zzz_eval, 1, dlgradbasis_z_eval, 1);

// lapl(rho) = 2 X . lapl(B) + 2 sum_c X_c . d_c B, so one term of
// its nuclear derivative contracts the BARE d_x B against
// 2 P lapl(B). That matrix is not otherwise formed, so build it.
xLmat = host_data.zmat.data() + 4 * spin_dim_scal * npts * nbe;
lwd->eval_xmat( npts, nbf, nbe, submat_map, xmat_fac, Ps, ldps,
lbasis_eval, nbe, xLmat, nbe, nbe_scr );
if( is_uks ) {
xZLmat = xLmat + npts * nbe;
lwd->eval_xmat( npts, nbf, nbe, submat_map, xmat_fac, Pz, ldpz,
lbasis_eval, nbe, xZLmat, nbe, nbe_scr );
}
}
if(is_rks)
lwd->eval_uvvar_mgga_rks( npts, nbe, basis_eval, dbasis_x_eval, dbasis_y_eval,
Expand Down Expand Up @@ -556,18 +570,54 @@ void ReferenceReplicatedXCHostIntegrator<ValueType>::
}

if( needs_laplacian ) {
const double vlapl_ipt = weights[ipt] * vlapl[ipt];
const double lbf = lbasis_eval[mu_i];
const double dlbx = dlgradbasis_x_eval[mu_i];
const double dlby = dlgradbasis_y_eval[mu_i];
const double dlbz = dlgradbasis_z_eval[mu_i];
d2_term_x = xN * dlbx + xNx * lbf + 2.0*d2_term_x;
d2_term_y = xN * dlby + xNy * lbf + 2.0*d2_term_y;
d2_term_z = xN * dlbz + xNz * lbf + 2.0*d2_term_z;

g_acc_x += vlapl_ipt * d2_term_x;
g_acc_y += vlapl_ipt * d2_term_y;
g_acc_z += vlapl_ipt * d2_term_z;
// The tau branch above leaves d2_term_* holding the Z term
// when polarized, so rebuild what this block needs rather
// than reuse it.
const double hN_x = d2bxx * xNx + d2bxy * xNy + d2bxz * xNz;
const double hN_y = d2bxy * xNx + d2byy * xNy + d2byz * xNz;
const double hN_z = d2bxz * xNx + d2byz * xNy + d2bzz * xNz;

// d/dA lapl(rho) = -2 [ X d_x lapl(B) + d_x B (fac P lapl(B))
// + 2 sum_c (hess B)_xc X_c ]
const double xL = xLmat[mu_i];
const double lN_x = xN * dlbx + dbx * xL + 2.0*hN_x;
const double lN_y = xN * dlby + dby * xL + 2.0*hN_y;
const double lN_z = xN * dlbz + dbz * xL + 2.0*hN_z;

if(is_rks) {
const double vlapl_ipt = weights[ipt] * vlapl[ipt];
g_acc_x += vlapl_ipt * lN_x;
g_acc_y += vlapl_ipt * lN_y;
g_acc_z += vlapl_ipt * lN_z;
} else {
// Same n / m_z transformation the LDA, GGA and tau blocks
// above use: rho_alpha = (rho_s + rho_z)/2.
const double vlaplp_ipt = weights[ipt] * vlapl[spin_dim_scal * ipt + 0];
const double vlaplm_ipt = weights[ipt] * vlapl[spin_dim_scal * ipt + 1];
const double vlapln_ipt = vlaplp_ipt + vlaplm_ipt;
const double vlaplz_ipt = vlaplp_ipt - vlaplm_ipt;

g_acc_x += 0.5 * vlapln_ipt * lN_x;
g_acc_y += 0.5 * vlapln_ipt * lN_y;
g_acc_z += 0.5 * vlapln_ipt * lN_z;

const double hZ_x = d2bxx * xZx + d2bxy * xZy + d2bxz * xZz;
const double hZ_y = d2bxy * xZx + d2byy * xZy + d2byz * xZz;
const double hZ_z = d2bxz * xZx + d2byz * xZy + d2bzz * xZz;

const double xZL = xZLmat[mu_i];
const double lZ_x = xZ * dlbx + dbx * xZL + 2.0*hZ_x;
const double lZ_y = xZ * dlby + dby * xZL + 2.0*hZ_y;
const double lZ_z = xZ * dlbz + dbz * xZL + 2.0*hZ_z;

g_acc_x += 0.5 * vlaplz_ipt * lZ_x;
g_acc_y += 0.5 * vlaplz_ipt * lZ_y;
g_acc_z += 0.5 * vlaplz_ipt * lZ_z;
}
}
}
}
Expand Down