Quantum simulation of carbon capture in periodic metal-organic frameworks

TL;DR

Addressing the challenge of predicting CO$_2$ adsorption in periodic MOFs, the paper uses Fe-MOF-74 as a test case to circumvent DFT limitations with a quantum-computing workflow. It reduces plane-wave bases to a compact active space by localizing Wannier orbitals and selecting MP2 natural orbitals, then applies a quantum-number preserving (QNP) ansatz within VQE, with SQD used for hardware validation. Classical simulations show the QNP approach reproduces full-CI-quality correlation energies in reduced spaces (e.g., $\Delta E^{\mathrm{QNPcorr}}_{AS} \approx \Delta E^{\mathrm{FCIcorr}}_{AS}$), and hardware experiments on IBM devices demonstrate feasibility up to ~28 qubits with self-consistent configuration recovery improving energy accuracy. This incremental quantum-computing workflow paves the way for predictive, quantum-accelerated design of carbon-capture materials in periodic systems.

Abstract

Carbon capture is vital for decarbonizing heavy industries such as steel and chemicals. Metal-organic frameworks (MOFs), with their high surface area and structural tunability, are promising materials for CO2 capture. This study focuses on Fe-MOF-74, a magnetic Mott insulator with exposed metal sites that enhance CO2 adsorption. Its strongly correlated electronic structure challenges standard DFT methods, which often yield inconsistent predictions. We initially benchmark adsorption energies using various DFT functionals, revealing substantial variability and underscoring the need for more accurate approaches, such as those provided by quantum computing. However, practical quantum algorithms are far less established for simulations of periodic materials, particularly when the plane-wave basis set, often comprising tens of thousands of basis vectors, is used. To address this, we employ an active space reduction strategy based on Wannier functions and natural orbital selection. Localized orbitals around the adsorption site are identified, and MP2 natural orbitals are used to improve convergence of correlation energies. Adsorption energies are then computed using a quantum number-preserving ansatz within the variational quantum eigensolver framework. In addition to classical simulations, we conduct quantum experiments using the sample-based quantum diagonalization method. Although current hardware limits the size of feasible simulations, our approach offers a more efficient and scalable path forward. These results advance the applicability of quantum algorithms to realistic models of carbon capture and periodic materials more broadly.

Figures (8)

• Figure 1: The Fe-MOF-74 model considered in this work (H white, C black, O red, Fe orange).
• Figure 2: The QNP fabric circuit proposed in Ref. anselmetti2021local.
• Figure 3: Convergence of the contribution of the MP2 correlation energy to the adsorption energy in the active space $\Delta E^{\mathrm{MP2}\mathrm{corr}}_{\mathrm{AS}}$ (see Eq. \ref{['eq:Eadscorr']}) as a function of the threshold used to truncate MP2 natural orbitals. Results are displayed for two different kinetic energy cutoffs used in the underlying Hartree-Fock calculation. The shaded area denotes the chemical accuracy interval around the most converged point obtained for a $10^{-7}$ threshold and 420 eV cutoff.
• Figure 4: Partial charges of the occupied orbitals included in the reduced active space of CO$_2$@MOF, MOF, and CO$_2$. The MOF and CO$_2$ orbitals are depicted on the side of the corresponding orbital in the adsorbed system. To simplify the visualization, only some of the atoms surrounding the adsorption site are displayed, but numerical calculations have been performed on the full periodic system.
• Figure 5: Partial charges of the unoccupied orbitals included in the reduced active space of CO$_2$@MOF, MOF, and CO$_2$. The MOF and CO$_2$ orbitals are depicted on the side of the corresponding orbital in the adsorbed system. To simplify the visualization, only some of the atoms surrounding the adsorption site are displayed, but numerical calculations have been performed on the full periodic system.