BH VQE — toward UHTC materials chemistry

Ultra-high-temperature ceramics (UHTCs) such as ZrB₂ and HfB₂ are critical for hypersonic vehicle thermal protection (X-51A, X-37B leading edges). Their electronic structure is challenging for classical ab initio methods due to strongly correlated transition-metal d-orbitals coupled to the boron σ-network — a natural target for variational quantum eigensolvers.

Full CAS-VQE on a ZrB₂ unit cell (~30 active spin-orbitals) is beyond current NISQ reach. BH is the simplest boron-containing molecule and the standard electron-correlation baseline in every boride computational study. This showcase establishes that Qubital's VQE pipeline reaches chemical-accuracy-adjacent precision on BH across the full dissociation curve — the direct prerequisite for scaling to CAS-VQE on the boride frontier orbital manifold in Phase II work.

BH in STO-3G minimal basis: 6 spatial orbitals × 2 spin = 12 spin-orbitals under Jordan-Wigner. Freezing the B 1s core drops to 10 active spin-orbitals; Bravyi-Kitaev with N + Sz symmetry conservation tapers to 8 qubits with ~276 Pauli terms. Hardware-efficient RY-CX ansatz at depth 3, ~32 parameters, L-BFGS-B multi-start optimizer with parameter-continuation across the bond-length sweep.

MolecularData generated via openfermionpyscf in a Linux Docker container (PySCF has no Windows wheels), then loaded from shipped HDF5 files at runtime — the platform runs natively on any workstation with no PySCF dependency. FCI references come from PySCF at each geometry for cross-check.