Quantitatively analyzing phonon spectral contribution of thermal conductivity based on nonequilibrium molecular dynamics simulations. II. From time Fourier transform

From a nanoscale heat transfer point of view, currently one of the most interesting and challenging tasks is to quantitatively analyze phonon mode specific transport properties in solid materials, which plays a vital role in many emerging and diverse technological applications. It has not been long that such information can be provided by the phonon spectral energy density (SED) or equivalently time domain normal mode analysis (TDNMA) methods in the framework of equilibrium molecular dynamics (EMD) simulations. However, few methods have been developed for nonequilibrium molecular dynamics (NEMD) simulations [Phys. Rev. B 91, 115426 (2015), 10.1103/PhysRevB.91.115426], the other widely used computational method for calculating thermal transport of materials in addition to EMD. In this work, a computational scheme based on time Fourier transform of atomistic heat current, called the frequency domain direct decomposed method (FDDDM), is proposed to analyze the contributions of frequency dependent thermal conductivity in NEMD simulations. The FDDDM results of Lennard-Jones argon and Stillinger-Weber Si are compared with the TDNMA method from EMD simulation. Similar trends are found for both cases, which confirm the validity of our FDDDM approach. Benefiting from the inherent nature of NEMD and the theoretical formula that does not require any temperature assumption, the FDDDM can be directly used to investigate the size and temperature effect. Moreover, the unique advantage of FDDDM prior to previous methods (such as SED and TDNMA) is that it can be straightforwardly used to characterize the phonon frequency dependent thermal conductivity of disordered systems, such as amorphous materials. The FDDDM approach can also be a good candidate to be used to understand the phonon behaviors and thus provides useful guidance for designing efficient structures for advanced thermal management.