Dynamical Insights into the Decomposition of 1,2-Dioxetane

Chemiluminescence in 1,2-dioxetane occurs through a thermally activated decomposition reaction into two formaldehyde molecules. Both ground-state and nonadiabatic dynamics (including singlet excited states) of the decomposition reaction have been simulated, starting from the first O-O bond-breaking transition structure. The ground-state dissociation occurs between t = 30 fs and t = 140 fs. The so-called entropic trap leads to frustrated dissociations, postponing the decomposition reaction. Specific geometrical conditions are necessary for the trajectories to escape from the entropic trap and for dissociation to be possible. The singlet excited states participate as well in the trapping of the molecule: dissociation including the nonadiabatic transitions to singlet excited states now occurs from t = 30 fs to t = 250 fs and later. Specific regions of the seam of the S0/S1 conical intersections that would "retain" the molecule for longer on the excited state have been identified

How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield of Dioxetane?

Chemiluminescence is the emission of light as a result of a nonadiabatic chemical reaction. The present work is concerned with understanding the yield of chemiluminescence, in particular how it dramatically increases upon methylation of 1,2-dioxetane. Both ground-state and nonadiabatic dynamics (including singlet excited states) of the decomposition reaction of various methyl-substituted dioxetanes have been simulated. Methyl-substitution leads to a significant increase in the dissociation time scale. The rotation around the O-C-C-O dihedral angle is slowed; thus, the molecular system stays longer in the "entropic trap" region. A simple kinetic model is proposed to explain how this leads to a higher chemiluminescence yield. These results have important implications for the design of efficient chemiluminescent systems in medical, environmental, and industrial applications

Mapping The Excited State Potential Energy Surface Of A Retinal Chromophore Model With Multireference And Equation-of-motion Coupled-cluster Methods

The photoisomerization of the retinal chromophore of visual pigments proceeds along a complex reaction coordinate on a multidimensional surface that comprises a hydrogen-out-of-plane (HOOP) coordinate, a bond length alternation (BLA) coordinate, a single bond torsion and, finally, the reactive double bond torsion. These degrees of freedom are coupled with changes in the electronic structure of the chromophore and, therefore, the computational investigation of the photochemistry of such systems requires the use of a methodology capable of describing electronic structure changes along all those coordinates. Here, we employ the penta-2,4-dieniminium (PSB3) cation as a minimal model of the retinal chromophore of visual pigments and compare its excited state isomerization paths at the CASSCF and CASPT2 levels of theory. These paths connect the cis isomer and the trans isomer of PSB3 with two structurally and energetically distinct conical intersections (CIs) that belong to the same intersection space. MRCISD+Q energy profiles along these paths provide benchmark values against which other ab initio methods are validated. Accordingly, we compare the energy profiles of MRPT2 methods (CASPT2, QD-NEVPT2, and XMCQDPT2) and EOM-SF-CC methods (EOM-SF-CCSD and EOM-SF-CCSD(dT)) to the MRCISD+Q reference profiles. We find that the paths produced with CASSCF and CASPT2 are topologically and energetically different, partially due to the existence of a locally excited region on the CASPT2 excited state near the Franck-Condon point that is absent in CASSCF and that involves a single bond, rather than double bond, torsion. We also find that MRPT2 methods as well as EOM-SF-CCSD(dT) are capable of quantitatively describing the processes involved in the photoisomerization of systems like PSB3

Computation of conical intersections by using perturbation techniques

Multiconfigurational second-order perturbation theory, both in its single-state multiconfigurational second-order perturbation theory (CASPT2) and multistate (MS-CASPT2) formulations, is used to search for minima on the crossing seams between different potential energy hypersurfaces of electronic states in several molecular systems. The performance of the procedures is tested and discussed, focusing on the problem of the nonorthogonality of the single-state perturbative solutions. In different cases the obtained structures and energy differences are compared with available complete active space self-consistent field and multireference configuration interaction solutions. Calculations on different state crossings in LiF, formaldehyde, the ethene dimer, and the penta-2,4-dieniminium cation illustrate the discussions. Practical procedures to validate the CASPT2 solutions in polyatomic systems are explored, while it is shown that the application of the MS-CASPT2 procedure is not straightforward and requires a careful analysis of the stability of the results with the quality of the reference wave functions, that is, the size of the active [email protected] [email protected] [email protected]

The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

Occupational advice for Patients undergoing Arthroplasty of the Lower limb: An intervention development and feasibility study (The OPAL Study)

Background Hip and knee replacements are regularly performed for patients who work. There is little evidence about these patients’ needs and the factors influencing their return to work. There is a paucity of guidance to help patients return to work after surgery and a need for structured occupational advice to enable them to return to work safely and effectively. Objective(s) To develop an occupational advice intervention to support early recovery to usual activities including work which is tailored to the requirements of patients undergoing hip and knee replacements. To test the acceptability, practicality and feasibility of this intervention within current care frameworks Design An intervention mapping (IM) approach was used to develop the intervention. The research methods employed were: rapid evidence synthesis; qualitative interviews with patients and stakeholders; prospective cohort study; survey of clinical practice; modified Delphi consensus process. The developed intervention was implemented and assessed during the final feasibility stage of the IM process. Setting Orthopaedic departments within NHS secondary care. Participants Patients in work, and intending to return to work following primary elective hip and knee replacement surgery; healthcare professionals and employers. Interventions Occupational advice intervention. Main outcome measures Development of an occupational advice intervention. Fidelity of the developed intervention when delivered in a clinical setting. Patient and clinician perspectives of the intervention. Preliminary assessments of intervention effectiveness and cost. Results A cohort study (154 patients), 110 stakeholder interviews, survey of practice (152 respondents) and evidence synthesis provided the necessary information to develop the intervention. The intervention included information resources, personalized return to work plan and co-ordination from the healthcare team to support the delivery of 13 patient and 20 staff performance objectives (POs). To support delivery, a range of tools (e.g. occupational checklists, patient workbooks, employer information), roles (e.g. return-to-work coordinator) and training resources were created. Feasibility was assessed in 21 of the 26 patients recruited from 3 NHS trusts. Adherence with the defined performance objectives was 75% for patient POs and 74% for staff POs. The intervention was generally well received although the short timeframe available for implementation and concurrent research evaluation led to some confusion amongst patients and those delivering the intervention regarding its purpose and the roles and responsibilities of key staff. Limitations Implementation and uptake of the intervention was not standardized and was limited by the study timeframe. Evaluation of the intervention involved a small number of patients which limited the ability to assess it. Conclusions The developed occupational advice intervention supports best practice. Evaluation demonstrated good rates of adherence against defined performance objectives. However, a number of operational and implementation issues require further attention Future work The intervention warrants a randomised controlled trial to assess its clinical and cost effectiveness to improve rates and timing of sustained return to work after surgery. This research should include the development of a robust implementation strategy to ensure adoption is sustained. Funding This project was funded by the NIHR Health Technology Assessment programme (project number 15/28/02) Trial Registrations International Standard Randomised Controlled Trials Number Trial ID: ISRCTN27426982 International prospective register of systematic reviews (PROSPERO) Registration: CRD4201604523