A Hybrid Mode-Space/Real-Space Scheme for DFT+NEGF Device Simulations

Density functional theory based simulation techniques enable thorough investigation of the operational characteristics of nanoscale devices regardless of their configurational complexity. However, this flexibility comes with considerable computational cost. In this work, we present a hybrid mode-space/real-space scheme that utilizes a mode-space basis to represent periodic contacts while maintaining the real-space representation of the central device region. Reducing the size of the contact blocks via mode-space approximation speeds up the calculation of the open boundary conditions and reduces the overall size of the Hamiltonian and overlap matrices, which leads to significant improvements in the computational efficiency of simulations. Keeping the real-space representation of the device blocks preserves the versatility and accuracy of the ab-initio approach. The merits of the proposed method are demonstrated with the simulation of an amorphous device with metallic contacts.