Kwant

Kwant is an open-source Python package for numerical quantum transport calculations. It provides a flexible framework for building tight-binding models of mesoscopic systems and computing their electronic transport properties from first principles. Kwant is designed to handle complex geometries, multi-terminal devices, and a range of lattice types, making it a popular tool in theoretical and computational condensed matter physics.

The core idea in Kwant is to model a physical structure as a tight-binding lattice with onsite energies and hopping terms. Users construct a system using a builder interface, selecting a lattice (such as square or honeycomb), and then adding sites and hoppings to represent the device. Leads, which model semi-infinite reservoirs, can be attached to the device to form two-terminal or multi-terminal geometries. Once the system is defined, it is finalized to produce an efficient representation suitable for numerical calculations.

Kwant provides tools to solve the scattering problem and extract transport properties. It computes quantities such as transmission probabilities, conductance via the Landauer formalism, and local observables like the local density of states and current distributions. Calculations can be performed at specific energies or over energy ranges, enabling the study of spectral and transport features across parameter sweeps.

Workflow typically involves defining a lattice, building the device with onsite and hopping terms, attaching leads, finalizing the system, and using solver routines to obtain transmission and other transport data. Kwant emphasizes a modular, extensible workflow and includes plotting utilities to visualize geometries and results. It is widely used in research and teaching for graphene, topological materials, quantum dots, and related mesoscopic systems.

Kwant is actively developed as an open-source project with comprehensive documentation, tutorials, and examples, and is supported by a community of researchers and contributors.