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We present the effect of next-nearest-neighbor hopping on Holstein polarons. The energy and wavefunction of the ground state and first excited state are obtained by using a conjugate-gradient technique on the variational Hilbert space of the electron-phonon (e-ph) system. We increase the size of the variational space systematically to obtain high accuracy. With the converged wavefunction at our disposal we obtain various physical quantities and correlation functions to get a holistic insight into the physics of e-ph interaction. Our study reveals that the effect of next-nearest-neighbor hopping is most prominent at the physically interesting crossover regime of the e-ph coupling and in the adiabatic regime. We have also performed analytical strong coupling second order perturbation with a Lang-Firsov (LF) phonon basis to account for some features in the strong coupling regime.

We report here a study of the effect of short-ranged ordering on the electronic structure and optical properties of CuZn alloys. We shall use the augmented space recursion technique developed by us in conjunction with the tight-binding linear muffin tin orbitals basis.

A new formalism using the ideas of the augmented space recursion (introduced by one of us) has been proposed to study the ground state properties of ordered and disordered one-dimensional Holstein model. For ordered case our method works equally well in all parametric regime and matches with the existing exact diagonalization and DMRG results. On the other hand, the quenched substitutionally disordered model works in low and intermediate regime of electron phonon coupling. Effect of phononic and substitutional disorder is treated on equal footing. r

In this paper we have studied the electronic structure of bcc FexCr1−x alloys in the ferromagnetic phase using three different techniques: augmented space recursion coupled with tight-binding linearized muffin-tin orbitals (TB-LMTO-ASR), the coherent potential approximation based on the Korringa–Kohn–Rostocker method (KKR-CPA) and the special quasi-random structure technique linked with the projector augmented wave (PAW-SQS). The aim was to provide a comparison between the different methods and examine their strengths and weaknesses vis-à-vis one another.