High precision evaluation of the combustion enthalpy by ab-intio computations

Accurate evaluation of combustion enthalpy is of high scientific and industrial importance. Although via ab-initio computation of heat of reactions, as one of the promising and well-established approaches in computational chemistry, this goal should in principle be achievable, examples of reliable and precise evaluation of heat of combustion by ab-initio methods has surprisingly not yet been reported. A handful of works carried out for this purpose report significant inconsistencies between the ab-initio evaluated and experimentally determined combustion enthalpies and suggest empirical corrections to improve the accuracy of predicted data. With this background, the main aims of the present study is to investigate the reasons behind those reported inconsistencies and propose guidelines for highly accurate evaluation of combustion enthalpy via ab-initio computations. Through the provided guidelines, the most accurate results ever reported, with average absolute deviation, mean unsigned error and correlation coefficient of 1.556 kJ/mole, 0.072% and 0.99999, respectively, is achieved for theoretically computed combustion enthalpies of 40 studied hydrocarbons.

Electride Characteristics of M2(h5-E5)2 (M= Be, Mg; E= Sb5-)

Ab initio computation is performed on the binuclear sandwich complexes, M 2 ( h 5 -Sb 5 ) 2 . Eclipsed and staggered conformations are generated due to the h 5 mode of binding by Sb 5 - ligand with the alkaline earth metals (Be and Mg metals). The complexes are thermodynamically stable at room temperature. The electron density descriptors and the natural bond orbital (NBO) analysis confirmed the covalent nature of the M-M bond. Both Be 2 ( h 5 -Sb 5 ) 2 and Mg 2 ( h 5 -Sb 5 ) 2 complexes have one non-nuclear attractor (NNA) at the center of the M-M bond which is predicted and confirmed by the electron density analysis. At the NNA the values of the Laplacian of electron density are negative and an electron localization function basin (ELF) is present at the center of the M-M bond for localized electrons. Both the complexes show large values of nonlinear optical properties (NLO). Both the designed binuclear sandwich complexes Be 2 ( h 5 -Sb 5 ) 2 and Mg 2 ( h 5 -Sb 5 ) 2 behave as electride.

Muonic Lithium atoms: nuclear structure corrections to the Lamb shift

In view of the future plans to measure the Lamb shift in muonic Lithium atoms we address the microscopic theory of the \mu\,μ-^66Li^{2+}2+ and \mu\,μ-^77Li^{2+}2+ systems. The goal of the CREMA collaboration is to measure the Lamb shift to extract the charge radius with high precision and compare it to electron scattering data or atomic spectroscopy to see if interesting puzzles, such as the proton and deuteron radius puzzles, arise. For this experiment to be successful, theoretical information on the nuclear structure corrections to the Lamb shift is needed. For \muμ-^66Li^{2+}2+ and \mu\,μ-^77Li^{2+}2+ there exist only estimates of nuclear structure corrections based on experimental data that suffer from very large uncertainties. We present the first steps towards an ab initio computation of these quantities using few-body techniques.

Ab initio computation for solid-state 31P NMR of inorganic phosphates: revisiting X-ray structures

The complete 31P NMR chemical shift tensors for 22 inorganic phosphates obtained from ab initio computation are found to correspond closely to experimentally obtained parameters. The cases where correspondence is significantly improved upon geometry optimization point to the crystal structures requiring correction.