A theoretical study of the low-lying electronic states of OIO and the ground states of IOO and OIO−

The Importance of Tight f Basis Functions for Heavy p-Block Oxides and Halides: A Parallel With Tight d functions in the Second Row

It is well-known that both wave function ab initio and DFT calculations on second-row compounds exhibit anomalously slow basis set convergence unless the basis sets are augmented with additional "tight" (high-exponent) d functions, as in the cc-pV(n+d)Z and aug-cc-pV(n+d)Z basis sets. This has been rationalized as being necessary for a better description of the low-lying 3d orbital, which as the oxidation state increases sinks low enough to act as a back-donation acceptor from chalcogen and halogen lone pairs. This prompts the question whether a similar phenomenon exists for the isovalent compounds of the heavy p-block. We show that for the fourth and fifth row, this is the case, but this time for tight f functions enhancing the description of the low-lying 4f and 5f Rydberg orbitals, respectively. In the third-row heavy p block, the 4f orbitals are too far up, while the 4d orbitals are adequately covered by the basis functions already present to describe the 3d subvalence orbitals.

Atmospheric chemistry of CF3O2: a theoretical study on mechanisms and pathways of the CF3O2 + IO reaction

The mechanisms and reaction pathways for the CF3O2 + IO reaction have been investigated by quantum chemistry methods. It has been found that the title reaction takes place on both the singlet and triplet potential energy surfaces (PES). On the singlet PES, the most important products include CF3OOOI, CF3OOIO, CF3OIO2, and CF2O + FIO2, while other products such as CF2O + FOIO, CF2O + FOOI, CF3OOI + O((3)P), CF3OI + O2 ((1)Δ and (3)Σ), and CF3O + OIO are negligible due to high barriers or unstable formations. On the triplet PES, CF3O + OIO is the dominant product with a lower barrier. As for FIO2 and it isomers, the most stable one is FIO2. TDDFT (Time Dependent Density Functional Theory) calculation indicates that CF3OOOI, CF3OOIO and CF3OIO2 undergo photolysis easily under sunlight. Moreover, a minor contribution relative to hydrogen is found in the CX3O2 + IO (X = H and F) reactions.

Is near-"spectroscopic accuracy" possible for heavy atoms and coupled cluster theory? An investigation of the first ionization potentials of the atoms Ga-Kr

Recent developments in ab initio coupled cluster (CC) theory and correlation consistent basis sets have ushered in an era of unprecedented accuracy when studying the spectroscopy and thermodynamics of molecules containing main group elements. These same developments have recently seen application to heavier inorganic or transition metal-containing species. The present work benchmarks conventional single reference coupled cluster theory (up to full configuration interaction for valence electron correlation and coupled cluster with up to full pentuple excitations (CCSDTQP) for core-valence correlation) and explicitly correlated coupled cluster methods [CC with single, double, and perturbative triple substitutions (CCSD(T)-F12)] for the atomic ionization potentials of the six 4p elements (Ga-Kr), a property with experimental error bars no greater than a few cm(-1). When second-order spin orbit coupling effects are included, a composite methodology based on CCSD(T) calculations yielded a mean signed error of just -0.039 kcal mol(-1) and a mean unsigned error of 0.043 kcal mol(-1). Inclusion of post-CCSD(T) correlation corrections reduced both of these values to -0.008 kcal mol(-1) and 0.025 kcal mol(-1), respectively, with the latter corresponding to an average error of just 9 cm(-1). The maximum signed error in the latter scheme was just -0.043 kcal mol(-1) (15 cm(-1)).