Analysis Of Multi-scale Transient Quantum Electromagnetic Coupling Method For Nanodevices

The interaction between charge and electromagnetic fields plays a crucial role in many new devices and materials.In practical nanoscale devices,quantum effects need to be considered from an atomic perspective,resulting in an increase in computational cost,making calculations limited to a small portion of the analog system.For a general semiconductor device,a complete system is commonly described by Maxwell's equations and drift-diffusion equations.When simulating nanoscale devices,this method cannot describe quantum effects and atomic details,a hybrid method which combines quantum mechanics(QM)and electromagnetics(EM)is therefore developed,so-called the QM/EM method.The QM/EM framework can be used to study the time-dependent transport properties of nanoscale devices.The research of this paper mainly focuses on the calculation method,combined with some applications.It is elaborated from two aspects.First,the calculation method of quantum electromagnetic hybrid simulation is given.The scalar potential and the vector magnetic position are used instead of the electric field and the magnetic field to express Maxwell's equations in the time domain.The equation of electron motion is solved by the time-dependent density functional based tight-binding method,therefore the response of electronic dynamics of the quantum mechanical region is obtained.When electromagnetic waves penetrate the quantum mechanical region,the entire system can use Maxwell's equation to uniformly determine the field distribution in the region,and combine the drift-diffusion equation to describe the charge transport of the system.The transient potential distribution calculated in the electromagnetic region is taken as the boundary condition in the quantum simulation,and the response current in the quantum region is substituted into the Maxwell's equations of the electromagnetic region.Thus,charge distribution,current density,and potential at different time steps and spatial scales are integrated within a unified computational framework.Among them,for the semiconductor device,the drift diffusion model is added to the electromagnetic region,and the implicit finite volume method is used to solve the problem;the quantum region is discretized by the classical fourth-order Runge-Kutta method,combined with the Green's function and the perturbation approximation method.Solve.Applying the QM/EM method to a nanoscale device based on quasi-one-dimensional graphene carbon nanotubes and two-dimensional carbon nitride materials,the current response curve of the device during operation can be given,thus the device is transmitted.Analysis of the nature of the transport.Second,the QM/EM method is optimized from the perspective of numerical solution.When the explicit method is used to solve the quantum region,the nonlinear problem is approximated as a linear problem by selecting a smaller time step.This method saves the time of quantum region calculation,but in the QM/EM framework,the semiconductor transport simulation of the electromagnetic region is also a nonlinear problem,so quantum and electromagnetic calculations can be unified into an implicit solution.When the quantum region is implicitly calculated,the self-consistent field method is introduced to solve the self-consistent iterative solution between the equation of motion and Poisson equation,which is unified with the time dispersion of the electromagnetic region calculation.The advantage of this method change is that for the quantum electromagnetic coupling model that needs to be calculated synchronously in time,the time steps of the two regions can be simultaneously amplified.Although the quantum region needs to consider self-consistent iteration,the calculation time of the electromagnetic region can be significantly reduced.The overall calculation steps are reduced,and the calculation time is further shortened,which is very helpful for expanding the calculation system.Based on this calculation framework,the time-dependent transport properties of carbon nanotube defects are further studied.The QM/EM method combines macroscale and microscale to provide a computational framework for studying the dynamic response of electronic devices at nanoscale.In the continuous optimization of the theory and calculation of the QM/EM method,it is expected that the method can be applied to a wider range of real electronic device research,providing a prediction and reference for the preparation of nanoscale devices.