Convergence of quantum transport calculations with respect to atomic basis sets: Application to graphene-based DNA sequencing

In the past decade, first-principles quantum charge transport calculations based on density-functional theory (DFT)-based non-equilibrium green’s function (NEGF) formalism have become one of the most powerful and routine computational tools in modern nano-scale research. The DFT-NEGF approach by its nature starts from the Hamiltonian matrices constructed based on spatially localized atomic-like bases sets. However, despite the critical role of the quality of localized basis sets on the accuracy of DFT-NEGF calculations, the correlations between the basis sets and quantum charge transport calculations has been insufficiently discussed. Specifically, a scheme to assess the numerical convergence of the transmission with respect to localized basis sets is still absent. In this presentation, by carrying out DFT-NEGF calculations for a DNA nucleobase placed within the nanogap between two graphene nanoribbon electrodes we systematically test the number and extension of atomic basis sets and find that unconverged or overcomplete atomic basis sets can produce significantly misleading quantum transport calculation data. We will finally present the practical guidelines of adopting localized basis sets to carry out accurate yet cost-effective ab initio quantum transport calculations.