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Villain-Lai-Das Sarma(VLDS)方程因其能够有效描述分子束外延生长过程而在表面生长动力学等领域中备受关注.然而,长程关联噪声驱动下的VLDS方程的标度结果尚不明确,不同解析近似方法所得的标度结果仍不自洽.在数值模拟方面,由于非线性项的存在,VLDS方程一直存在数值发散的问题.当前主要引入指数衰减技术替换非线性项以缓解数值发散的问题,但是最近研究表明,这种方法会导致所获得的标度指数发生歧变.因此本文基于深度神经网络来表征VLDS方程中的各个确定项,并基于数值稳定型神经网络分别对含长程时间和空间关联噪声的VLDS系统进行有效的数值模拟.结果表明,我们所构建的深度神经网络具有良好的数值计算稳定性和泛化性,可以获得不同关联噪声驱动下的VLDS方程的可靠标度指数.同时,本文还发现长程时间关联噪声驱动的VLDS系统在时间关联指数较大时呈现谷堆状的表面形貌,而空间关联噪声驱动下的表面形貌则仍然呈现自仿射分形结构.
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关键词:
- 神经网络 /
- MBE生长 /
- Villain-Lai-Das Sarma方程 /
- 动力学标度
The Villain-Lai-Das Sarma (VLDS) equation has achieved significant attention in surface growth dynamics due to its effective description of Molecular Beam Epitaxy (MBE) growth processes. However, the scaling exponents of the VLDS equation driven by long-range correlated noise remain unclear, as different analytical approximation methods have yielded inconsistent results. The nonlinear term in the VLDS equation presents a challenge for numerical simulation methods, often leading to issues of numerical divergence. Existing numerical approaches primarily employ exponential decay techniques to replace nonlinear terms to alleviate the numerical divergence. However, recent studies have shown that these methods may change the scaling exponents and universality class of the growth system. Therefore, we propose a novel deep neural network-based method to address this issue. First, we construct a fully convolutional neural network to characterize the deterministic terms in the VLDS equation. To train the neural network, we generate training data with traditional finite-difference method before numerical divergence occurs. Then, we train the neural network to represent the deterministic terms, and perform simulations of VLDS driven by long-range temporally and spatially correlated noises based on the neural networks. The simulation results demonstrate that the deep neural networks constructed here possess good numerical stability. It can obtain reliable scaling exponents for the VLDS equation driven by different uncorrelated and correlated noises. Furthermore, this work also discovers that the VLDS system with long-range temporal correlation exhibits mound-shaped morphologies when the temporal correlation exponent is large enough, while the growing surface driven by spatially correlated noise still remains self-affine fractal structure independence on the spatial correlation exponent.-
Keywords:
- Neural network /
- MBE growth /
- Villain-Lai-Das Sarma equation /
- Dynamic scaling
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