AI 中文总结
该研究为LAMMPS开发了满足涨落耗散定理的三温度原子自旋-晶格动力学扩展，经多基准及GdFeCo全光开关验证，确立了其作为超快磁学定量模拟平台的价值。
AI 中文摘要
诸如VAMPIRE之类的原子自旋动力学（ASD）代码在刚性晶格上模拟飞秒激光诱导的超快退磁和全光开关（AOS）；而大规模原子/分子 massively 并行模拟器（LAMMPS）的SPIN软件包则同时传播自旋和晶格，但直到现在只能将其自旋热浴耦合到单一全局温度，无法进行三温度（3TM）模拟。我们提出了一个经过验证的3TM扩展，包含两个新的修正：langevin/spin/ttm，将随机自旋热浴与fix ttm的局域电子温度场耦合；以及moment/scale/spin，为异质矩系统提供所需的每个原子矩相关（1/μ_i） prefactor，其确定性项按1/μ_i缩放，且根据涨落耗散定理，随机噪声按1/√μ_i缩放。我们在单物种基准上验证该框架：进动、体心立方铁（bcc-Fe）居里曲线、连续退磁-再磁化-进动轨迹，以及仅自旋ASD代码无法实现的晶格应变声子脉冲；随后使用文献参数（Radu/Ostler交换常数、矩和阻尼）对钆铁钴（GdFeCo）的热诱导AOS进行验证。修正后的积分器再现了实验报道的瞬态类铁磁亚晶格排列、与场无关的热开关、在真实8×8文献阻尼相图上接近1的开关概率、在T_e^0≈2000 K以上消失的非单调临界冷却持续时间边界、以角动量补偿为中心的成分相关开关窗口，以及系统规模收敛与单调物理阻尼依赖性。这些结果确立了LAMMPS作为超快磁学三温度自旋-晶格模拟的定量验证平台。
英文摘要
Atomistic spin dynamics (ASD) codes like VAMPIRE simulate femtosecond-laser-induced ultrafast demagnetization and all-optical switching (AOS) on a rigid lattice; the SPIN package of the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) instead propagates spins and lattice together, but until now could couple its spin thermostat only to a single global temperature, precluding three-temperature (3TM) simulations. We present a validated 3TM extension with two new fixes: langevin/spin/ttm, coupling the stochastic spin bath to the local electron-temperature field of fix ttm; and moment/scale/spin, supplying the per-atom moment-dependent ($1/μ_i$) prefactor required for heterogeneous-moment systems, with deterministic terms scaling as $1/μ_i$ and, as required by the fluctuation-dissipation theorem, stochastic noise scaling as $1/\sqrt{μ_i}$. We validate the framework on single-species benchmarks-precession, the bcc-Fe Curie curve, a continuous demagnetization-remagnetization-precession trajectory, and a lattice-strain acoustic-phonon pulse unavailable to spin-only ASD codes-then on heat-induced AOS of GdFeCo with literature parameters (Radu/Ostler exchange constants, moments, and damping). The corrected integrator reproduces the experimentally reported transient ferromagnetic-like sublattice alignment, field-insensitive thermal switching, a switching probability approaching unity across a genuine 8x8 literature damping phase diagram, a non-monotonic critical-cooling-duration boundary that disappears above $T_e^0 \approx 2000 \text{ K}$, a composition-dependent switching window centered on angular-momentum compensation, and convergence in system size with monotonic, physical damping dependence. These results establish LAMMPS as a quantitatively validated platform for three-temperature spin-lattice simulations of ultrafast magnetism.
