A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-b]benzot...

A first-principles embedding theory that combines the salient features of density functional theory ~DFT! and traditional quantum chemical methods is presented. The method involves constructing a DFT-based embedding potential and then using it as a one-electron operator within a very accurate ab initio calculation. We demonstrate how DFT calculations can be systematically improved via this proc...

Density functional theory(DFT) and Hartree-Fock(HF) calculations are reported for the family of transition metal fluorides ScF3, TiF4, VF5, and CrF6. Both HF and the local-density-aproximation (LDA) yield excellent agreement with experimental bond lengths, while the B-LYP gradient-corrected density functional gives bond lengths 0.04 − 0.05 Å too long. An investigation of various combinations of...

OVERVIEW: Density functional theory (DFT) is the most widely used ab initio method in material simulations. It accounts for 75% of the NERSC allocation time in the material science category. The DFT can be used to calculate the electronic structure, the charge density, the total energy and the atomic forces of a material system. With the advance of the HPC power and new algorithms, DFT can now ...

A systematic vibrational spectroscopic assignment and analysis of pregabalin has been carried out by using FTIR, FT-Raman spectral data. The vibrational analysis were aided by electronic structure calculations-hybrid density functional methods (B3LYP) performed with 631G(d,p) basis set. Molecular equilibrium geometries, electronic energies, natural bond order analysis, IR intensities, and harmo...

The widely employed DFT+U formalism is known to give rise to many self-consistent yet energetically distinct solutions in correlated systems, which can be highly problematic for reliably predicting the thermodynamic and physical properties of such materials. Here we study this phenomenon in the bulk materials UO2, CoO, and NiO, and in a CeO2 surface. We show that the following factors affect wh...

We present a new scheme to include the van der Waals (vdW) interactions in approximated Density Functional Theory (DFT) by combining the quantum harmonic oscillator model with the maximally localized Wannier function technique. With respect to the recently developed DFT/vdW-WF2 method, also based on Wannier Functions, the new approach is more general, being no longer restricted to the case of w...

The results of density-functional theory (DFT) calculations of the energy barriers for three lowbarrier relaxation processes in Ag/Ag(100) growth edge-zipping, atom-attraction and downward funneling (DF) are presented and compared with embedded atom method (EAM) calculations. In general, we find good agreement between the DFT values for these processes and the values assumed in recent simulatio...

Large-scale simulations of plastic deformation and phase transformations in alloys require reliable classical interatomic potentials. We construct an embedded-atom method potential for niobium as the first step in alloy potential development. Optimization of the potential parameters to a well-converged set of density-functional theory DFT forces, energies, and stresses produces a reliable and t...