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Sheng-Jie Zhang

Publications and source records attributed to Sheng-Jie Zhang.

3 recordsLinked to original sources

Augmented Lagrangian Method for Mathematical Programs with Second-Order Cone Complementarity Constraints

This paper investigates mathematical programs with second-order cone complementarity constraints (SOCMPCCs), which extend classical mathematical programs with complementarity constraints (MPCCs) by incorporating second-order cone structures. SOCMPCCs present significant theoretical and computational challenges, primarily due to the failure of standard constraint qualifications (such as Robinson's constraint qualification) at all feasible points. This difficulty hinders the direct application of classical nonlinear programming theories and algorithms. Motivated by the success of the augmented Lagrangian method (ALM) in solving MPCCs, we explore its extension to SOCMPCCs. The ALM, known for its matrix-free implementation and strong local convergence properties, is well suited for handling the intricate interplay between complementarity and second-order cone constraints. In this paper, we propose a tailored ALM algorithm framework for SOCMPCCs and establish its feasibility and convergence properties. We show that, under bounded ALM penalty parameters or bounded augmented Lagrangian functions, the generated sequence converges to feasible points of the SOCMPCC. Furthermore, under feasibility and additional SOCMPCC-nondegeneracy condition, we prove convergence to K-stationary points, which constitute a fundamental optimality condition for SOCMPCCs. Numerical experiments, including both illustrative examples and high-dimensional problems, are conducted to demonstrate the effectiveness and practical applicability of the proposed algorithm in addressing the challenges inherent in SOCMPCCs.

math.OC

Ultrafast charge ordering by self-amplified exciton-phonon dynamics in TiSe$_2$

The origin of charge density waves (CDW) in TiSe$_2$ has long been debated, mainly due to the difficulties in identifying the timescales of how and when the excitonic pairing and electron-phonon coupling (EPC) come into play. Without a proper time resolution and microscopic mechanism, one has to assume simultaneous appearance of CDW and periodic lattice distortions (PLD). Here, we accomplish a complete separation of exciton and PLD dynamics and unravel their interplay in the ultrafast time domain in our real-time time-dependent density functional theory simulations. We find that laser pulses knock off the exciton order and induce a homogeneous bonding-antibonding transition in the initial 20 fs, then the weakened electronic order triggers ionic movements antiparallel to the original PLD. The EPC comes into play after the initial 20~fs, and the two processes mutually amplify each other leading to a complete inversion of CDW ordering. The self-amplified dynamics reproduces the evolution of band structures in excellent agreement with ultrafast photoemission experiment. Hence we resolve the key processes in the initial dynamics of CDW that help elucidate the mechanism underlying the long debated problem.

cond-mat.mes-hall

Cooperative evolution of intraband and interband excitations for high harmonic generation in strained MoS2

Modulating electronic structure of two-dimensional (2D) materials represents an exciting avenue for tailoring their optoelectronic properties. Here, we identify a strain-induced, cooperative effect of intraband and interband excitations contributing to high harmonic generation (HHG) in prototype dichalcogenide MoS2 monolayer. We find that besides the dominant intraband contributions, interband current is also indispensable in modulating HHG. The HHG yields increase linearly with the compressive strain since flatter band dispersion and Berry curvature enhance both interband and intraband dynamics. Band structure can be retrieved with high reliability by monitoring the strain-induced evolution of HHG spectra, suggesting that strain not only provides an additional knob to control HHG in solids, but also marks a way towards a complete understanding of underlying microscopic mechanisms.

cond-mat.mes-hall