Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

An implementation of the reverse Monte Carlo algorithm is presented for the study of amorphous tetrahedral semiconductors. By taking into account a number of constraints that describe the tetrahedral bonding geometry along with the radial distribution function, we construct a model of amorphous silicon using the reverse Monte Carlo technique. Starting from a completely random configuration, we generate a model of amorphous silicon containing 500 atoms closely reproducing the experimental static structure factor and bond angle distribution and in improved agreement with electronic properties. Comparison is made to existing reverse Monte Carlo models, and the importance of suitable constraints beside experimental data is stressed.

The full-potential all-electron linearized augmented plane wave plus local orbital method, as implemented in the suite of the software WIEN2K, has been used to systematically investigate the structural, electronic, and magnetic properties of the actinide compounds AnN ($\mathrm{An}=\mathrm{Ac}$, Th, Pa, U, Np, Pu, and Am). The theoretical formalism used is the generalized gradient approximation to density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional. Each compound has been studied at the nonmagnetic, ferromagnetic, antiferromagnetic configurations, all with and without spin-orbit coupling (SOC). The structural parameters, bulk moduli, densities of states, and charge distributions have been computed and compared to available experimental data and other theoretical calculations published in the literature. Our total energy calculations clearly indicate that AcN, ThN, and PaN are nonmagnetic, while the ground states of UN, NpN, PuN, and AmN are found to be ferromagnetic. The influence of SOC in the actinide nitrides is found to be significant. The nature of the interactions between the actinide metals and nitrogen atom and the implications on $5f$ electron delocalization and localization are discussed in detail.

From density-functional calculations, we show that localized states stemming from defects or topological disorder exhibit an anomalously large electron–phonon coupling. We provide a simple analysis to explain the observation and perform a detailed study on an interesting system: amorphous silicon. We compute first-principles deformation potentials (by computing the sensitivity of specific electronic eigenstates to individual classical normal modes of vibration). We also probe thermal fluctuations in electronic eigenvalues by first-principles thermal simulation. We find a strong correlation between a static property of the network (localization, as gauged by inverse participation ratio (IPR)) and a dynamical property (the amplitude of thermal fluctuations of electron energy eigenvalues) for localized electron states. In particular, both the squared electron–phonon coupling and the variance of energy eigenvalues are proportional to the IPR of the localized state. We compare the results for amorphous Si to photoemission experiments. While the computations are carried out for silicon, very similar effects have been seen in other systems with disorder.