Fix an out-of-bound read in XC module at dft_functional=HF

[maki49]

Fix #5404

[Copilot]

Pull request overview

This PR addresses issue #5404 by preventing out-of-bounds reads in the XC gradient-correction path when dft_functional=HF leaves XC_Functional::func_id empty, which previously could yield a non-zero “phantom” XC energy/potential for nspin=2.

Changes:

• Added guards to skip gradient-correction routines when func_id is empty (HF / no (semi-)local functional configured).
• Hardened func_id indexing by checking func_id.size() before accessing func_id[1], and added a safe fallback when only one functional ID is present.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
source/source_hamilt/module_xc/xc_grad.cpp	Adds func_id.empty() early-return and guards func_id[1] access in gradcorr.
source/source_hamilt/module_xc/xc_gga_wrap.cpp	Adds func_id.empty() guards in gcx_spin/gcc_spin and avoids OOB by selecting func_id[1] only when present.

Suppressed comments (1)

source/source_hamilt/module_xc/xc_grad.cpp:61

• The new early-return when func_id is empty skips initializing stress_gga for is_stress==true. Callers like source/source_pw/module_pwdft/stress_gga.cpp index stress_gga[0..8] after gradcorr returns, so leaving the vector empty will cause an out-of-bounds access (e.g., HF sets func_type=4 but leaves func_id empty).

    if(func_id.empty())
    {
        return;
    }

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