6. Phonons and Thermoelectric properties

Frozen phonon calculations represent a computational methodology within the realm of condensed matter physics and materials science. This technique is employed to investigate the vibrational characteristics of crystalline materials, with a particular focus on phonons—quantized vibrational modes in a crystal lattice. Phonons play a pivotal role in determining diverse physical properties of materials, including thermal conductivity and lattice thermal expansion.

In the NanoDCAL code, the vibrational spectra can be obtained using density functional theory (DFT) in a cluster configuration at equilibrium [WWG], with the Hessian matrix that is evaluate using a finite differencing method in a supercell [NDH].

Moreover, one of the most important questions concerning charge transport in molecular electronic devices is the role of electron-phonon (e-p) interaction. Here, “phonon” refers to quantized molecular vibrational modes which couple to various scattering states of the device.

A general formulation for the time-averaged thermal and thermoelectric properties of materials is derived within the nonequilibrium Green’s function theory, which provides a starting point for further numerical calculations of these properties[CDH]_.