As a minimal model of the chromophore of rhodopsin proteins, the penta-2,4-dieniminium cation (PSB3) poses a challenging test system for the assessment of electronic-structure methods for the exploration of ground- and excited-state potential-energy surfaces, the topography of conical intersections, and the dimensionality (topology) of the branching space. Herein, we report on the performance of the approximate linear-response coupled-cluster method of second order (CC2) and the algebraic-diagrammatic-construction scheme of the polarization propagator of second and third orders (ADC(2) and ADC(3)). For the ADC(2) method, we considered both the strict and extended variants (ADC(2)-s and ADC(2)-x). For both CC2 and ADC methods, we also tested the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) variants. We have explored several ground- and excited-state reaction paths, a circular path centered around the S1/S0 surface crossing, and a 2D scan of the potential-energy surfaces along the branching space. We find that the CC2 and ADC methods yield a different dimensionality of the intersection space. While the ADC methods yield a linear intersection topology, we find a conical intersection topology for the CC2 method. We present computational evidence showing that the linear-response CC2 method yields a surface crossing between the reference state and the first response state featuring characteristics that are expected for a true conical intersection. Finally, we test the performance of these methods for the approximate geometry optimization of the S1/S0 minimum-energy conical intersection and compare the geometries with available data from multireference methods. The present study provides new insight into the performance of linear-response CC2 and polarization-propagator ADC methods for molecular electronic spectroscopy and applications in computational photochemistry.

Rhodium, a 4d transition metal and a lighter analogue of iridium, is known to exhibit its highest VIth oxidation state in RhF 6 molecule. In this report, the stability and decomposition pathways of two species containing rhodium at a potentially formal +IX oxidation state, [RhO 4 ] + and RhNO 3 , have been investigated theoretically within the framework of the relativistic twocomponent Hamiltonian calculations. Possible rearrangement into isomers featuring lower formal oxidation numbers has been explored. We found that both species studied are metastable with respect to elimination of O 2 or NO. However, the local minima containing Rh(IX) are protected by sufficient energy barriers on the decomposition pathway, and they could in principle be prepared. The analysis of a broader set of compounds containing group 8 and 9 metals in high formal oxidation states that correspond to the group number showed that, in contrast to a standard trend, the limits of formally attainable oxidation state correlate with high level of covalent bonding character in the complexes studied.

This work commemorates the 150th anniversary of Mendeleyev's Periodic Table of Elements.Abstract: Theoretical calculations utilizingr elativistic ZORA Hamiltonian point to the conceivable existence of an IrNO 3 molecule in C 3v geometry.T his minimum is shown to correspond to genuine nonavalent iridium nitride trioxide, whichi saneutrala nalogue of cationic [IrO 4 ] + speciesd etected recently.D espite the presence of nitride anion,the molecule is protected by substantial barriers exceeding 200 kJ mol À1 against transformations leading, for example, to global minimum (O=) 2 IrÀNO, which contains metal at al ower formal oxidation state.In recent years, some unusualf ormal oxidation states of metals,t hat is, Hg IV , [1,2] Cs V , [3][4][5] and Pu VIII[6] or U XII[7] were studied theoretically,and some wereestablishede xperimentally.Anoctavalents tate has traditionally been considered the highest achievableo xidation state of chemicale lements, as exemplified by Ru VIII , [8][9][10] Os VIII , [8][9][10] or Xe VIII[11] in their tetraoxides,a nd other relateds toichiometries. Exactly half ac entury ago Jørgensen pointed out that, if the formal oxidation state + IX existed, it would be in ac ompound of iridium. [12] Because IrO 4 has one unpaired valencee lectron in the d-shell, ar elated [IrO 4 ] + monocation became the naturalc andidate for investigations. Indeed, in 1996 Kiselev and co-workerss howed that the minimum potential energy surfacef or this cation corresponded to the isomeric form of [IrO4] + in which the metal atom has af ormal oxidation state of + IX. [13,14] In 2010, the thermochemical stability of oxidation level + IX in an [IrO 4 ] + cation was theoretically predicted by Himmel et al. using electronic structure calculations. [15] Four years later,t he abovementioned cation was reliably detected using time-of-flight photodissociation spectroscopy. [16] It is worth mentioning that much earlier,i n1 969, Rother et al. provided Mçssbauer isomer [a] Dr.

We report the results of high-pressure Raman spectroscopy studies of alkali metal fluoroargentates (M2AgF4, where M = Na, K, Rb) combined with theoretical and X-ray diffraction studies for the K member of the series. Theoretical density functional calculations predict two structural phase transitions for K2AgF4: one from low-pressure monoclinic P21/c (beta) phase to intermediate-pressure tetragonal I42d structure at 6 GPa, and another to high-pressure triclinic P1 phase at 58 GPa. However, Raman spectroscopy and X-ray diffraction data indicate that both polymorphic forms of K2AgF4, as well as two other fluoroargentate phases studied here, undergo amorphization at pressures as low as several GPa.

To account for systematic error of CASPT2 method empirical modification of the zeroth-order Hamiltonian with Ionization Potential-Electron Affinity (IPEA) shift was introduced. The optimized IPEA value (0.25 a.u.), called standard IPEA (S-IPEA), was recommended but due to its unsatisfactory performance in multiple metallic and organic compounds it has been questioned lately as a general parameter working properly for all molecules under CASPT2 study. As we are interested in Schiff bases of retinal, an important question emerging from this conflict of choice, to use or not to use S-IPEA, is whether the introduction of the modified zeroth-order Hamiltonian into CASPT2 ansatz does really improve their energetics. To achieve this goal, we assessed an impact of the IPEA shift value, in a range of 0-0.35 a.u., on vertical excitation energies to low-lying singlet states of two protonated (RPSBs) and two unprotonated (RSBs) Schiff bases of retinal for which experimental data in gas phase are available. In addition, an effect of geometry, basis set, and active space on computed VEEs is also reported. We find, that for these systems, the choice of S-IPEA significantly overestimates both S →S and S →S energies and the best theoretical estimate, in reference to the experimental data, is provided with either unmodified zeroth-order Hamiltonian or small value of the IPEA shift in a range of 0.05-0.15 a.u., depending on active space and basis set size, equilibrium geometry, and character of the excited state. © 2018 Wiley Periodicals, Inc.