arXiv subjects

Zhe-Bin Guan

Publications and source records attributed to Zhe-Bin Guan.

5 recordsLinked to original sources

arXiv2026

Accelerating ab initio spin-phonon relaxation simulation of single-ion magnets by quantum embedding and spatial truncation

Single-ion magnets (SIMs) show promise for high-density storage and quantum computing, but predicting spin-phonon coupling (SPC) and magnetic relaxation remains challenging due to the need for numerous non-equilibrium multiconfigurational calculations. Recent advances in quantum embedding methods offer a potential route to address this issue. In this work, density matrix embedding theory (DMET) combined with complete active space self-consistent field (CASSCF) is benchmarked for the static magnetic properties and spin-phonon coupling (SPC) parameters of Dy$^{3+}$-based SIMs. The method is further combined with spatial truncation to calculate SPC parameters for these SIMs. It is found that truncating the space near the first coordination sphere reduces the computational cost dramatically while keeping the errors in the effective energy barrier and relaxation time-scale negligible. This study provides a practical calculation framework for accurate and efficient spin dynamics prediction, laying the foundation for the rational design of high-performance single-molecule magnets.

physics.chem-ph↗

arXiv2026

State-Averaged Density Matrix Embedding Theory for Local Excitations

Density matrix embedding theory (DMET) provides an elegant framework in quantum chemistry to describe local properties of chemical systems that allows a high-level method being used to solve an embedded subsystem constructed based on a low-level treatment of the whole system, and therefore achieves a balance between efficiency and accuracy. However, because the embedded subspace in DMET is typically constructed from the mean-field ground state Slater determinant, the resulting bath orbitals inherently favor the ground state, leading to unbalanced descriptions of ground and excited states for local excitations. In this work, we first demonstrate the starting-point dependence of DMET in excitation energy calculations, and then generalize original ground-state based DMET by extending the starting point from the single Slater determinant to state-averaged (SA) complete active space self-consistent field (CASSCF), hence termed as SA-DMDT. In calculations of magnetic anisotropy and excitation energies of transition metal and lanthanide complexes, SA-DMET shows significant improvement in accuracy compared to the single-state DMET. Configuration-averaged Hartree-Fock (CAHF), which is equivalent to SA-CASSCF when all states in the chosen active space are equally averaged, is found to give comparable accuracy as a DMET starting point, thus offering a more efficient choice for state-averaged embedding. Finally, the recently proposed non-orthongal atomic-orbital-based DMET (AO-DMET) is tested on various systems and gives very promising results in all cases. These results establish SA-DMET, especially in combination with AO-DMET and CAHF, as a robust and efficient embedding framework for local excited states in strongly correlated metal complexes.

physics.chem-ph↗

arXiv2026

Impurity-Preserved Density Matrix Embedding Theory for Local Electronic Excitations

Density matrix embedding theory (DMET), which is usually based on a Schmidt decomposition of Slater determinants by partitioning the full system into impurity and environment in terms of local orthogonal orbitals (LOs), has demonstrated considerable promise in electronic structure studies because it enables the extraction of local properties using a high-level solver within an embedded impurity subsystem with greatly reduced degrees of freedom, thereby achieving a balance between accuracy and computational cost. However, its application to excited states of strongly correlated systems, such as lanthanide complexes, remains challenging because the errors relative to all-electron results can still be significant. Motivated by the success of the previously developed atomic orbitals (AOs) based DMET framework (Ai, Li, and Jiang, Phys. Rev. Lett. 2025, 135, 026502.), termed AO-DMET, which attains improved accuracy by constructing the embedded subspace based on a non-orthogonal decomposition of the Slater determinant in terms of AOs, we propose a new LO-based partitioning scheme that fully preserves the impurity space spanned by corresponding AOs and can achieve accuracy closely matching that of AO-DMET while retaining the orthogonal partition and its associated computational efficiency. The performance of the proposed method is demonstrated through excitation energy calculations for several representative lanthanide complexes. These results establish an efficient and accurate partitioning scheme for describing excited states in strongly correlated systems within the DMET framework.

physics.chem-ph↗

arXiv2025

Density-Matrix Embedding Based Multi-Configurational Perturbation Theory Approach to Single-Ion Magnets

Multi-configurational wave-function theory (MC-WFT) that combines complete active space self-consistent field (CASSCF) approach with subsequent state interaction (SI) treatment of spin-orbit coupling (SOC), abbreviated as CASSCF-SO, plays important roles in microscopic understanding of single-ion magnets (SIMs) with different central transition metal or lanthanide ions and various coordination environments, but its application to SIMs with complex structure is severely limited due to its highly demanding computational cost. Density-matrix embedding theory (DMET) provides a systematic and mathematically rigorous framework to combine low-level mean field approaches like Hartree-Fock and high-level MC-WFT methods like CASSCF-SO, which is particularly promising to SIMs. As a continuation of our previous work on DMET+CASSCF for $3d$ SIMs (Ai, Sun, and Jiang, J. Phys. Chem. Lett. 2022, 13, 10627), we extend the methodology by considering dynamic correlation on top of CASSCF using the second-order $n$-electron valence perturbation theory (NEVPT2) in the DMET framework, abbreviated as DMET+NEVPT2, and benchmark the accuracy of this approach to molecular magnetic anisotropy in a set of typical transition metal complexes. We found that DMET+NEVPT2 can give the results very close to all-electron treatment, and can be systematically improved for higher accuracy by expanding the region treated as the central cluster, while the computation cost is dramatically reduced due to the reduction of the number of orbitals by DMET construction. Our findings suggest that DMET is capable of accounting for most of the dynamic correlation that is important for magnetic anisotropy in typical SIMs, and can be useful for further high-accuracy spin-phonon study and high-throughput computations.

physics.chem-ph↗

arXiv2025

Density Matrix Embedding Theory-Based Multi-Configurational Quantum Chemistry Approach to Lanthanide Single-Ion Magnets

Accurate and efficient theoretical descriptions of lanthanide systems based on ab initio electronic structure theory remain highly challenging due to the complex interplay of strong electronic correlation and significant relativistic effects in 4f electrons. The composite multi-configurational quantum chemistry method, which combines the complete active space self-consistent field (CASSCF) approach with subsequent state interaction (SI) treatment of spin-orbit coupling (SOC), abbreviated as CASSI-SO, has emerged as the preferred method for ab initio studies of lanthanide systems. However, its widespread application is hindered by its substantial computational cost. Building on the success of integrating density-matrix embedding theory (DMET) with CASSI-SO in our previous theoretical study of 3d single-ion magnets (SIMs) (Ai, Sun, and Jiang, J. Phys. Chem. Lett. 2022, 13, 10627), we now extend the DMET+CASSI-SO approach to lanthanide SIM systems. We provide a detailed formulation of the regularized direct inversion of iterative subspace (R-DIIS) algorithm, which ensures obtaining physically correct restricted open-shell Hartree-Fock (ROHF) wavefunctions, a critical factor for the effectiveness of DMET. Additionally, we introduce the subspace R-DIIS (sR-DIIS) algorithm, which proves to be more efficient and robust for lanthanide systems. Using several representative lanthanide single-ion magnets (4f-SIMs) as test cases, we demonstrate the performance of these new algorithms and highlight the exceptional accuracy of the DMET+CASSI-SO approach. We anticipate that this enhanced DMET+CASSI-SO methodology will significantly advance large-scale theoretical investigations of complex lanthanide systems.

physics.chem-ph↗