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Two-dimensional layered materials, in general, and transition metal dichalcogenides, in particular, are promising as future device materials. Vanadium based dichalcogenides, i.e., VX2 (X = S, Se, and Te) are special in the class for showing a wide range of intriguing properties. Depending on the structural phases, VX2 can be metallic or semiconducting. The T-phase, i.e., the metallic one, is well known to host some exotic electronic properties like the charge density wave, anomalous Hall effect, ferromagnetism, etc., having strong bearing as an electronic device material. The H-phase, on the other hand, is also predicted to show ferromagnetism. The materials show properties strongly dependent on their physical dimensionality, a clear manifestation of quantum confinement effects. Several experimental attempts successfully demonstrated chemical and bio-medical applications also of this class of materials. Moreover, the heterostructures formed by VX2 with other electronically dissimilar materials could bring more variation in their existing properties. Therefore, the study of VX2 materials provides a fertile ground to explore several fascinating physical phenomena and their possibilities in future applications. Here, in the present paper, we have tried to review the current scenario in this particular field by highlighting some recent key findings. The paper is aimed at providing some insight into the recent theoretical and experimental achievements in this direction, especially in the context of electronic and magnetic properties in their lower physical dimensionality. This could furnish a comprehensive guiding tour toward exploration in the journey through VX2 materials.

The recently developed AFOT code is applied to investigate the two-photon-absorbing (TPA) properties of some of the bis(styryl) benzene derivatives (BSBD) demonstrated recently to possess large TPA cross sections. The results are compared both with the earlier semi-empirical as well as the more recent density functional calculations.

We present an AM1 semi-empirical study of the two-photon absorption (TPA) properties of a number of bis (styryl)benzene derivatives. In a recent report these systems were shown to be good two-photon absorbers. An analysis based on the INDO scheme was also included to calculate the TPA properties. The present study, based on configuration interaction consisting of single and double excitations, is compared with the above INDO model with respect to the prediction of energetics and TPA properties. The results indicate qualitative agreement, but serious questions regarding the applicability of both methods remain.

Metal-semiconductor (Schottky barrier) and semiconductor-semiconductor (heterojunction) interfaces show rectifying barrier heights and band offsets, which are two key quantities required to optimize the performance of a device. A large number of models and empirical theories have been put forward by various workers in the field during the last 50 years. But a proper understanding of the microscopic origin of these quantities is still missing. In this article, our focus is mainly to present a unified framework for first principles investigation of the electronic structure of epitaxial interfaces, in which one of the constituents is a semiconductor. LMTO method is now a well established tool for self-consistent electronic structure calculations of solids within LDA. Such calculations, when performed on supercell geometries, are quite successful in predicting a wide range of interface specific electronic properties accurately and efficiently. We describe here the basic formalism of this LMTO-supercell approach in its various levels of sophistication and apply it to investigate the electronic structure of A- and B-type NiSi2/Si(111) interface as a prototype metal-semiconductor system, and CaF2/Si(111) interface as a prototype insulator-semiconductor system. These are a few of the most ideal lattice matched epitaxial interfaces whose atomic and electronic structures have been extensively studied using a wide range of experimental probes. We give here a glimpse of these experimental results and discuss the success as well as limitations of LDA calculations to achieve accuracies useful for the device physicists.

A time‐dependent analog of the Born–Oppenheimer approximation is derived. The resulting wave function furnishes an alternative route to obtain the vibronic corrections to the frequency‐dependent nonlinear optical effects.

The electronic structures of ${\mathrm{NiSi}}_{2}$/Si(111) A- and B-type interfaces are calculated within the local density approximation (LDA) using large supercells and the LMTO full-potential and ASA methods. The Schottky-barrier heights for the two interfaces differ by 0.14 eV, in agreement with experiment. The difference is caused by a partly filled interface band present in both structures. The LDA barrier heights ${E}_{F}$-${E}_{v}$ are both 0.4 eV too low, and insensitive to interface relaxations and to external potentials. The correct density-functional expression for the barrier height is ${E}_{F}$-${E}_{v}$+\ensuremath{\Delta}${v}_{\mathrm{xc}}$, where \ensuremath{\Delta}${v}_{\mathrm{xc}}$ is a nonlocal correction.

The authors have delineated certain important aspects of the use of theoretical Compton profiles for estimating cohesive energy, energy of mixing, etc. Inclusion of electron-electron correlation in the calculation of Compton profiles seems to be essential in order to get the correct values of ground state energy differences. Some model calculations have also been performed for the energy change as a result of 'switching on' correlation in a homogeneous electron gas at zero temperature. Numerical estimates of this 'correlation energy' have been obtained for free-electron-like metals, viz Na and Li.

The Pattison-Williams method of using Fourier-transformed Compton profiles for obtaining Fermi momenta in simple metals, is extended to set up a scheme for inferringd orf band occupancies in transition metals, rare earths etc. CP measurements are reported for Ni,α-Mn andβ-Mn and then the new scheme is applied to obtain 3d occupancies in these systems. Some comments on the use of this method for other systems are also made.