arXiv subjects

Zhigang Shuai

Publications and source records attributed to Zhigang Shuai.

At least 19 recordsLinked to original sources

arXiv2026

The Counterintuitive "One-Enhanced, One-Suppressed" Bifurcation Phenomenon of Spin Mobility under Weak Spin-Orbit Coupling in Helices

The chiral-induced spin selectivity (CISS) effect poses a longstanding puzzle: how weak spin-orbit coupling (SOC) within a helical molecule produces strong spin polarization. We uncover a counterintuitive phenomenon, a "one-enhanced, one-suppressed" bifurcation of spin-resolved mobility relative to the SOC-free case. We trace this phenomenon to an analytical sign reversal of spin-dependent transmission and identify it as the microscopic origin of CISS. The phenomenon is found absent in achiral systems and single-stranded DNA, validating our theoretical picture. Our findings resolve the core puzzle and establish the origin of CISS.

cond-mat.other↗

arXiv2026

Layer-Controlled Intermolecular Coupling and Many-Body Effects in C$_{60}$ Films

Crystalline C$_{60}$ is a molecular solid whose electronic properties emerge from the interplay of intermolecular hopping, electron correlations, and electron-vibration coupling. Unlike moir$\rm\acute{e}$ van der Waals heterostructures, where interaction strength is commonly tuned by twist angle, molecular materials offer a complementary route in which layer number, molecular orientation, and substrate registry provide experimentally accessible control parameters. Here we present a systematic thickness-dependent angle-resolved photoemission study of C$_{60}$ films, spanning the monolayer to the bulk limit. The HOMO-derived band exhibits a non-monotonic evolution: the intermediate-thickness film shows larger bandwidth, reduced effective mass, and pronounced gap-like and sub-band features. The experimental trends, together with Holstein-model simulations, point to strengthened effective intermolecular electronic coupling and enhanced electron-phonon-induced spectral renormalization in the intermediate-thickness regime. These results identify a dimensional crossover in C$_{60}$ films and establish layer number as an effective knob for engineering electronic structure and many-body interactions in molecular thin films.

cond-mat.mtrl-sci↗

arXiv2025

Quantum Machine Learning of Molecular Energies with Hybrid Quantum-Neural Wavefunction

Quantum computational chemistry holds great promise for simulating molecular systems more efficiently than classical methods by leveraging quantum bits to represent molecular wavefunctions. However, current implementations face significant limitations in accuracy due to hardware noise and algorithmic constraints. To overcome these challenges, we introduce a hybrid framework that learns molecular wavefunction using a combination of an efficient quantum circuit and a deep neural network. This approach enhances computational efficiency and accuracy, surpassing traditional quantum computational chemistry methods. Numerical benchmarking on molecular systems shows that our hybrid quantum-neural wavefunction approach achieves near-chemical accuracy, comparable to advanced quantum and classical techniques. Experimental validation on a superconducting quantum computer, using the isomerization reaction of cyclobutadiene, further demonstrates its practical applicability, with high accuracy in energy estimation and significant resilience to noise.

quant-ph↗

arXiv2024

Optimal Tree Tensor Network Operators for Tensor Network Simulations: Applications to Open Quantum Systems

Tree tensor network states (TTNS) decompose the system wavefunction to the product of low-rank tensors based on the tree topology, serving as the foundation of the multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) method. In this work, we present an algorithm that automatically constructs the optimal and exact tree tensor network operators (TTNO) for any sum-of-product symbolic quantum operator.The construction is based on the minimum vertex cover of a bipartite graph. With the optimal TTNO, we simulate open quantum systems such as spin relaxation dynamics in the spin-boson model and charge transport in molecular junctions. In these simulations, the environment is treated as discrete modes and its wavefunction is evolved on equal footing with the system. We employ the Cole-Davidson spectral density to model the glassy phonon environment, and incorporate temperature effects via thermo field dynamics. Our results show that the computational cost scales linearly with the number of discretized modes, demonstrating the efficiency of our approach.

quant-ph↗

arXiv2023

Roles of non-local electron-phonon coupling on the electrical conductivity and Seebeck coefficient: a TD-DMRG study

Organic molecular materials are potential high-performance thermoelectric materials. Theoretical understanding of thermoelectric conversion in organic materials is essential for rational molecular design for efficient energy conversion materials. In organic materials, non-local electron-phonon coupling plays a vital role in charge transport and leads to complex transport mechanisms, including hopping, phonon-assist current, band, and transient localization. In this work, based on time-dependent density matrix renormalization group (TD-DMRG) method, we look at the role of non-local electron-phonon coupling on the thermoelectric conversion in organic systems described by Holstein-Peierls model. We calculate the current-current correlation and the heat current-current correlation functions. We find that (i) non-local electron-phonon coupling has very weak influence on Seebeck coefficient because of the cancellation between heat current-current correlation function and the current-current correlation function, but it has strong influence on conductivity through dynamic disorders; (ii) doping concentration has a strong influence on both conductivity and Seebeck coefficient significantly, and the optimal doping ratio to reach the highest power factor is 3%-10% fillings.

cond-mat.mtrl-sci↗

arXiv2023

Quantum Dynamical Approach to Predicting the Optical Pumping Threshold for Lasing in Organic Materials

We present a quantum dynamic study on organic lasing phenomena, which is a challenging issue in organic optoelectronics. Previously, phenomenological method has achieved success in describing experimental observation. However, it cannot directly bridge the laser threshold with molecular electronic structure parameters and cavity parameters. Quantum dynamics method for describing organic lasing and obtaining laser threshold is highly expected. In this Letter, we first propose a microscopic model suitable for describing the lasing dynamics of organic molecular system and we apply the time-dependent wave-packet diffusion (TDWPD) to reveal the microscopic quantum dynamical process for the optical pumped lasing behavior. Lasing threshold is obtained from the onset of output as a function of optical input pumping. We predict that the lasing threshold has an optimal value as function of the cavity volume and depends linearly on the intracavity photon leakage rate. The structure-property relationships between molecular electronic structure parameters (including the energy of molecular excited state, the transition dipole and the organization energy) and the laser threshold obtained through numerical calculations are in qualitative agreement the experimental results, which also confirms the reliability of our approach. This work is beneficial to understanding the mechanism of organic laser and optimizing the design of organic laser materials. TOC

physics.chem-ph↗

arXiv2023

TenCirChem: An Efficient Quantum Computational Chemistry Package for the NISQ Era

TenCirChem is an open-source Python library for simulating variational quantum algorithms for quantum computational chemistry. TenCirChem shows high performance on the simulation of unitary coupled-cluster circuits, using compact representations of quantum states and excitation operators. Additionally, TenCirChem supports noisy circuit simulation and provides algorithms for variational quantum dynamics. TenCirChem's capabilities are demonstrated through various examples, such as the calculation of the potential energy curve of $\textrm{H}_2\textrm{O}$ with a 6-31G(d) basis set using a 34-qubit quantum circuit, the examination of the impact of quantum gate errors on the variational energy of the $\textrm{H}_2$ molecule, and the exploration of the Marcus inverted region for charge transfer rate based on variational quantum dynamics. Furthermore, TenCirChem is capable of running real quantum hardware experiments, making it a versatile tool for both simulation and experimentation in the field of quantum computational chemistry.

quant-ph↗

arXiv2023

Efficient Quantum Simulation of Electron-Phonon Systems by Variational Basis State Encoder

Digital quantum simulation of electron-phonon systems requires truncating infinite phonon levels into $N$ basis states and then encoding them with qubit computational basis. Unary encoding and the more compact binary/Gray encoding are the two most representative encoding schemes, which demand $\mathcal{O}(N)$ and $\mathcal{O}(\log{N})$ qubits as well as $\mathcal{O}(N)$ and $\mathcal{O}(N\log{N})$ quantum gates respectively. In this work, we propose a variational basis state encoding algorithm that reduces the scaling of the number of qubits and quantum gates to both $\mathcal{O}(1)$ for systems obeying the area law of entanglement entropy. The cost for the scaling reduction is a constant amount of additional measurement. The accuracy and efficiency of the approach are verified by both numerical simulation and realistic quantum hardware experiments. In particular, we find using one or two qubits for each phonon mode is sufficient to produce quantitatively correct results across weak and strong coupling regimes. Our approach paves the way for practical quantum simulation of electron-phonon systems on both near-term hardware and error-corrected quantum computers.

quant-ph↗

arXiv2022

Unified definition of exciton coherence length for exciton-phonon coupled molecular aggregates

Exciton coherence length (ECL) is an essential concept to characterize the nature of exciton in molecular aggregates for photosynthesis, organic photovoltaics, and light-emitting diodes. ECL has been defined in a number of ways through the variance or purity of the electronic reduced density matrix. However, we find that these definitions fail to present a monotonic relationship with respect to the exciton radiative decay efficiency as it should be when exciton-phonon couplings are taken into accounts. We propose a unified definition of ECL by virtue of sum rule of oscillator strengths. Using the numerically accurate time-dependent matrix product states formalism applied to Frenkel-Holstein models for molecular aggregates in both one- and two-dimensional system, we find our ECL definition exhibits a monotonic relationship with respect to the radiative efficiency and can serve as an efficient and unified description for exciton coherence. We further predict that the two-dimensional aggregates can display maximum superradiance enhancement (SRE) at finite temperature, different from the previous knowledge of SRE-$1/T$ behavior.

physics.chem-ph↗

arXiv2022

Hybrid Quantum-Classical Boson Sampling Algorithm for Molecular Vibrationally Resolved Electronic Spectroscopy with Duschinsky Rotation and Anharmonicity

Using a photonic quantum computer for boson sampling has been demonstrated a tremendous advantage over classical supercomputers. It is highly desirable to develop boson sampling algorithms for realistic scientific problems. In this work, we propose a hybrid quantum-classical sampling (HQCS) algorithm to calculate the optical spectrum for complex molecules considering anharmonicity and Duschinsky rotation (DR) effects. The classical sum-over-state method for this problem has a computational complexity that exponentially increases with system size. In the HQCS algorithm, an intermediate harmonic potential energy surface (PES) is created, bridging the initial and final PESs. The magnitude and sign (-1 or +1) of the overlap between the initial state and the intermediate state are estimated by quantum boson sampling and by classical algorithms respectively, achieving an exponential speed-up. Additionally, the overlap between the intermediate state and the final state is efficiently evaluated by classical algorithms. The feasibility of HQCS is demonstrated in calculations of the emission spectrum of a Morse model as well as pyridine molecule by comparison with the nearly exact time-dependent density matrix renormalization group solutions. A near-term quantum advantage for realistic molecular spectroscopy simulation is proposed.

quant-ph↗

arXiv2021

Non-Markovian Stochastic Schrödinger Equation: Matrix Product State Approach to the Hierarchy of Pure States

We derive a stochastic hierarchy of matrix product states (HOMPS) for non-Markovian dynamics in open quantum system at finite temperature, which is numerically exact and efficient. HOMPS is obtained from the recently developed stochastic hierarchy of pure states (HOPS) by expressing HOPS in terms of formal creation and annihilation operators. The resulting stochastic first order differential equation is then formulated in terms of matrix product states and matrix product operators. In this way the exponential complexity of HOPS can be reduced to scale polynomial with the number of particles. The validity and efficiency of HOMPS is demonstrated for the spin-boson model and long chains where each site is coupled to a structured, strongly non-Markovian environment.

quant-ph↗

arXiv2021

Toward Practical Quantum Embedding Simulation of Realistic Chemical Systems on Near-term Quantum Computers

Quantum computing has recently exhibited great potentials in predicting chemical properties for various applications in drug discovery, material design, and catalyst optimization. Progress has been made in simulating small molecules, such as LiH and hydrogen chains of up to 12 qubits, by using quantum algorithms such as variational quantum eigensolver (VQE). Yet, originating from limitations of the size and the fidelity of near-term quantum hardware, how to accurately simulate large realistic molecules remains a challenge. Here, integrating an adaptive energy sorting strategy and a classical computational method, the density matrix embedding theory, which effectively finds a shallower quantum circuit and reduces the problem size, respectively, we show a means to circumvent the limitations and demonstrate the potential toward solving real chemical problems. We numerically test the method for the hydrogenation reaction of C6H8 and the equilibrium geometry of the C18 molecule, with basis sets up to cc-pVDZ (at most 144 qubits). The simulation results show accuracies comparable to those of advanced quantum chemistry methods such as coupled-cluster or even full configuration interaction, while the number of qubits required is reduced by an order of magnitude (from 144 qubits to 16 qubits for the C18 molecule) compared to conventional VQE. Our work implies the possibility of solving industrial chemical problems on near-term quantum devices.

quant-ph↗

arXiv2021

A General Charge Transport Picture for Organic Semiconductors with Nonlocal Electron-Phonon Couplings

The nonlocal electron-phonon couplings in organic semiconductors responsible for the fluctuation of intermolecular transfer integrals has been the center of interest recently. Several irreconcilable scenarios coexist for the description of the nonlocal electron-phonon coupling, such as phonon-assisted transport, transient localization, and band-like transport. Through a nearly exact numerical study for the carrier mobility of the Holstein-Peierls model using the matrix product states approach, we locate the phonon-assisted transport, transient localization and band-like regimes as a function of the transfer integral ($V$) and the nonlocal electron-phonon couplings ($ΔV$), and their distinct transport behaviors are analyzed by carrier mobility, mean free path, optical conductivity and one-particle spectral function. We also identify an "intermediate regime" where none of the established pictures applies, and the generally perceived hopping regime is found to be at a very limited end in the proposed regime paradigm.

cond-mat.mtrl-sci↗

arXiv2020

A General Automatic Method for Optimal Construction of Matrix Product Operators Using Bipartite Graph Theory

Constructing matrix product operators (MPO) is at the core of the modern density matrix renormalization group (DMRG) and its time dependent formulation. For DMRG to be conveniently used in different problems described by different Hamiltonians, in this work we propose a new generic algorithm to construct the MPO of an arbitrary operator with a sum-of-products form based on the bipartite graph theory. We show that the method has the following advantages: (i) It is automatic in that only the definition of the operator is required; (ii) It is symbolic thus free of any numerical error; (iii) The complementary operator technique can be fully employed so that the resulting MPO is globally optimal for any given order of degrees of freedom; (iv) The symmetry of the system could be fully employed to reduce the dimension of MPO. To demonstrate the effectiveness of the new algorithm, the MPOs of Hamiltonians ranging from the prototypical spin-boson model and Holstein model to the more complicated ab initio electronic Hamiltonian and the anharmonic vibrational Hamiltonian with sextic force field are constructed. It is found that for the former three cases, our automatic algorithm can reproduce exactly the same MPOs as the optimally hand-crafted ones already known in the literature.

physics.chem-ph↗

arXiv2020

Finite Temperature TD-DMRG for the Carrier Mobility of Organic Semiconductors

A large number of non-adiabatic dynamical studies have been applied to reveal the nature of carrier transport in organic semiconductors with different approximations. We present here a "nearly exact" graphical process unit (GPU) based finite temperature TD-DMRG method to evaluate the carrier mobility in organic semiconductors as described by electron-phonon model, in particular to rubrene crystal, one of the prototypical organic semiconductors, with parameters derived from first-principles. We find that (i) TD-DMRG is a general and robust method that can bridge the gap between hopping and band picture covering a wide range of electronic coupling strength; and (ii) with realistic parameters, TD-DMRG is able to account for the experimentally observed "band-like" transport behavior ($\partial μ/ \partial T < 0$) in rubrene. We further study the long-standing puzzle of isotope effect for charge transport and unambiguously demonstrate that the negative isotope effect ($\partial μ/ \partial m < 0$ where $m$ is the atomic mass) should be universal.

cond-mat.mtrl-sci↗

arXiv2019

Numerical Assessment for Accuracy and GPU Acceleration of TD-DMRG Time Evolution Schemes

Time dependent density matrix renormalization group (TD-DMRG) has become one of the cutting edge methods of quantum dynamics for complex systems. In this paper, we comparatively study the accuracy of three time evolution schemes in TD-DMRG, the global propagation and compression method with Runge-Kutta algorithm (P&C-RK), the time dependent variational principle based methods with matrix unfolding algorithm (TDVPMU) and with projector-splitting algorithm (TDVP-PS), by performing benchmarks on the exciton dynamics of Fenna-Matthews-Olson (FMO) complex. We show that TDVP-MU and TDVP-PS yield the same result when the time step size is converged and they are more accurate than P&C-RK4, while TDVP-PS tolerates a larger time step size than TDVP-MU. We further adopt the graphical processing units (GPU) to accelerate the heavy tensor contractions in TD-DMRG and it is able to speed up the TDVP-MU and TDVP-PS schemes by up to 73 times.

physics.chem-ph↗

arXiv2019

General Approach To Compute Phosphorescent OLED Efficiency

Phosphorescent organic light-emitting diodes (PhOLEDs) are widely used in the display industry. In PhOLEDs, cyclometalated Ir(III) complexes are the most widespread triplet emitter dopants to attain red, e.g., Ir(piq)3 (piq = 1-phenylisoquinoline), and green, e.g., Ir(ppy)3 (ppy = 2-phenylpyridine), emissions, whereas obtaining operative deep-blue emitters is still one of the major challenges. When designing new emitters, two main characteristics besides colors should be targeted: high photostability and large photoluminescence efficiencies. To date, these are very often optimized experimentally in a trial-and-error manner. Instead, accurate predictive tools would be highly desirable. In this contribution, we present a general approach for computing the photoluminescence lifetimes and efficiencies of Ir(III) complexes by considering all possible competing excited-state deactivation processes and importantly explicitly including the strongly temperature-dependent ones. This approach is based on the combination of state-of-the-art quantum chemical calculations and excited-state decay rate formalism with kinetic modeling, which is shown to be an efficient and reliable approach for a broad palette of Ir(III) complexes, i.e., from yellow/orange to deep-blue emitters.

physics.chem-ph↗

arXiv2018

Time-Dependent Density Matrix Renormalization Group Algorithms for Nearly Exact Absorption and Fluorescence Spectra of Molecular Aggregates at Both Zero and Finite Temperature

We implement and apply time-dependent density matrix renormalization group (TD-DMRG) algorithms at zero and finite temperature to compute the linear absorption and fluorescence spectra of molecular aggregates. Our implementation is within a matrix product state/operator framework with an explicit treatment of the excitonic and vibrational degrees of freedom, and uses the locality of the Hamiltonian in the zero-exciton space to improve the efficiency and accuracy of the calculations. We demonstrate the power of the method by calculations on several molecular aggregate models, comparing our results against those from multi-layer multiconfiguration time- dependent Hartree and n-particle approximations. We find that TD-DMRG provides an accurate and efficient route to calculate the spectrum of molecular aggregates.

physics.chem-ph↗