Theory of Electrons and Phonons

The team is headed by Prof. G P Srivastava. Our research interests range across many aspects of theoretical studies of the physics of electrons and phonons in bulk semiconductors, their surfaces, and nanostructures. Some of the basic theoretical concepts have been presented in the following books: The Physics of Phonons, 1st Edition (Adam Hilger --> Taylor and Francis, 1990); Theoretical Modelling of Semiconductor Surfaces -- Microscopic studies of electrons and phonons (World Scientific, 1999); Length Dependent Phonon Interactions (Springer, 2014); The Physics of Phonons, 2nd Edition (Taylor and Francis, 2022).

 

 

• Phonon engineering of nanocomposite thermoelectric materials
  G P Srivastava, Iori Thomas, Ceyda Yelgel, and Jawaher AlOtaibi
   
• Electronic and thermal properties of graphene
  G P Srivastava, Celal Yelgel, and Ayman Alofi
   
• Nanostructures: atomic and electronic structure
  G P Srivastava, R. H. Miwa, and A. B. McLean
   
• Solid surfaces: atomic geometry, electronic structure, and phonon modes
  G P Srivastava, Ali Z. AlZahrani and HM Tütüncü.
   
• Non-equilibrium phonon dynamics in bulk and low-dimensional semiconductors
  G P Srivastava.
   
• Electron-phonon coupling in BCS-type superconductors
  G P Srivastava and HM Tütüncü.
   

We have developed several computational/theoretical tools for studying these systems, which allow us to perform state-of-the-art research and to publish at the highest level. Notably, we have our own ab initio plane-wave pseudopotential LDA code, known as EKSETER, with which we carry out large-scale supercell calculations for structural determination and lattice dynamics. We have also developed a simplified quasiparticle approach which allows us to address problems related to excited electronic states. Bulk and surface phonon dispersion relations are studied either using a linear response scheme within the pseudopotential method, and also by employing an Adiabatic Bond Charge model. We have developed a detailed theory of three-phonon interactions, and two theories of lattice thermal conductivty (viz. Complementary Variational Principles, and a Model Relaxation Time approach). We have also developed an empirical pseudopotential code, based on a layer boundary matching scheme, which can be employed to study electronic states in superlattices and quantum wells. This method can also be employed when the structure is subjected to an external electric and/or magnetic field. <\p>

More recntly, we have developed model Hamiltonians for anharmonic phonon interactions, including acoustic as well as optical phonons, in bulk and nanocomposite materials. Using this Hamiltonian we can examine the role of `mini-Umklapp' anharmonic phonon interactions on the lattice thermal conductivity of nanocomposite materials. We have also developed model Hamiltonians to treat mass smudging and broken bonds at nanoscale interfaces. This development allows us to examine the role of these interface effects in controlling reduction in the lattice thermal conductivty of nanocomposite materials.

In another development, we have employ a semi-continuum elastic model to examine the phonon conductivity tensor in monolayer graphene, multi-layer graphen and graphite.

 

SUMMARY OF RESULTS OF THE LEVERHULME TRUST FUNDED RESEARCH RPG-2016-186

SUMMARY OF RESULTS OF THE EPSRC FUNDED RESEARCH EP-H046690-1

SUMMARY OF RESULTS OF THE LEVERHULME TRUST FUNDED RESEARCH F/00144/AS

SUMMARY OF RESULTS OF THE EPSRC FUNDED RESEARCH EP/D005191/1