Chemical binding

About: Chemical binding is a research topic. Over the lifetime, 1822 publications have been published within this topic receiving 52516 citations.

Chemical accuracy from quantum Monte Carlo for the Benzene Dimer

Abstract: We report an accurate study of interactions between benzene molecules using variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) methods. We compare these results with density functional theory using different van der Waals functionals. In our quantum Monte Carlo (QMC) calculations, we use accurate correlated trial wave functions including three-body Jastrow factors and backflow transformations. We consider two benzene molecules in the parallel displaced geometry, and find that by highly optimizing the wave function and introducing more dynamical correlation into the wave function, we compute the weak chemical binding energy between aromatic rings accurately. We find optimal VMC and DMC binding energies of −2.3(4) and −2.7(3) kcal/mol, respectively. The best estimate of the coupled-cluster theory through perturbative triplets/complete basis set limit is −2.65(2) kcal/mol [Miliordos et al., J. Phys. Chem. A 118, 7568 (2014)]. Our results indicate that QMC methods give chemical accuracy for weakly bound van der Waals molecular interactions, comparable to results from the best quantum chemistry methods.

Highly electrical resistive SiTiNx heating layers and diffusion barriers for PCRAM

Abstract: Highly electrical resistive amorphous SiTiNx films were explored as both heating layers and diffusion barriers for the cells of phase-change random-access memory (PCRAM). The measured electrical resistivity of SiTiNx films, determined by the nitrogen content x tunable up to 38.68%, is between 0.039–0.69 Ω cm which fulfils the requirements of a suitable heating layer suggested by simulations. SiTiNx films with a medium range of nitrogen content showed excellent thermal stability, very smooth surface and amorphous structure sustaining until at least 800 °C, thus suitable for application in PCRAM. However, SiTiNx films exhibit a high degree of temperature dependent resistivity, and show a different temperature coefficient of resistance with different N contents at the temperature range 400–500 °C. The chemical binding characteristics of SiTiNx films with such higher electrical resistivity were also investigated. The binding energy of Ti 2p spectra in SiTiNx films changes with nitrogen content and shifts to higher energies confirming their susceptibility to oxidation. Besides, interface analysis showed that these films perform excellently as a diffusion barrier between a W bottom electrode and the Ge2Sb2Te5 phase-change layer after evaluation annealing at 600 °C for 30 min.

The electron density distributions in hydride molecules: iii. hydrogen fluoride

Abstract: An electron density distribution is determined for the hydrogen fluoride molecule in its equilibrium configuration by requiring the distribution to predict the correct dipole moment and to exert forces on the nuclei equal and opposite to the nuclear forces of repulsion. The ability of the density function to give good estimates of the expectation values of other one-electron operators is found to be satisfactory. It is shown that an electron population analysis of the orbital densities, when interpreted in terms of the electronic forces which these densities exert on the nuclei, is of value in the understanding of chemical binding.