14 research outputs found
Coupled cluster theory on modern heterogeneous supercomputers
This study examines the computational challenges in elucidating intricate chemical systems, particularly through ab-initio methodologies. This work highlights the Divide-Expand-Consolidate (DEC) approach for coupled cluster (CC) theory—a linear-scaling, massively parallel framework—as a viable solution. Detailed scrutiny of the DEC framework reveals its extensive applicability for large chemical systems, yet it also acknowledges inherent limitations. To mitigate these constraints, the cluster perturbation theory is presented as an effective remedy. Attention is then directed towards the CPS (D-3) model, explicitly derived from a CC singles parent and a doubles auxiliary excitation space, for computing excitation energies. The reviewed new algorithms for the CPS (D-3) method efficiently capitalize on multiple nodes and graphical processing units, expediting heavy tensor contractions. As a result, CPS (D-3) emerges as a scalable, rapid, and precise solution for computing molecular properties in large molecular systems, marking it an efficient contender to conventional CC models
Epidemiology of Invasive Fungal Infections in Latin America
The pathogenic role of invasive fungal infections (IFIs) has increased during the past two decades in Latin America and worldwide, and the number of patients at risk has risen dramatically. Working habits and leisure activities have also been a focus of attention by public health officials, as endemic mycoses have provoked a number of outbreaks. An extensive search of medical literature from Latin America suggests that the incidence of IFIs from both endemic and opportunistic fungi has increased. The increase in endemic mycoses is probably related to population changes (migration, tourism, and increased population growth), whereas the increase in opportunistic mycoses may be associated with the greater number of people at risk. In both cases, the early and appropriate use of diagnostic procedures has improved diagnosis and outcome
A Macrocyclic 1,4-Diketone Enables the Synthesis of a <i>p</i>‑Phenylene Ring That Is More Strained than a Monomer Unit of [4]Cycloparaphenylene
The
synthesis of a <i>p</i>-terphenyl-based macrocycle,
containing a <i>p</i>-phenylene unit with 42.6 kcal/mol
of strain energy (SE), is reported. The conversion of a macrocyclic
1,4-diketone to a highly strained arene system takes place over five
synthetic steps, featuring iterative dehydrative reactions in the
aromatization protocol. Spectroscopic data of the deformed benzenoid
macrocycle are in excellent agreement with other homologues that have
been reported, indicating that the central <i>p</i>-phenylene
ring of <b>9</b> is aromatic
PIMOM_Vibrational_XYZ.zip
These are folders containing the xyz coordinates for the molecules used in the paper. </p
Good Vibrations: Calculating Excited-State Frequencies Using Ground-State Self-Consistent Field Models
The use of Δ-self-consistent field (SCF) approaches
for studying
excited electronic states has received a renewed interest in recent
years. In this work, the use of this scheme for calculating excited-state
vibrational frequencies is examined. Results from Δ-SCF calculations
for a set of representative molecules are compared with those obtained
using configuration interaction with single substitutions (CIS) and
time-dependent density functional theory (TD-DFT) methods. The use
of an approximate spin purification model is also considered for cases
where the excited-state SCF solution is spin-contaminated. The results
of this work demonstrate that an SCF-based description of an excited-state
potential energy surface can be an accurate and cost-effective alternative
to CIS and TD-DFT methods
Photoelectron Spectra of Gd2O2− and Non-Monotonic Photon-Energy Dependent Variations in Populations of Close-Lying Neutral States
Photoelectron spectra of Gd2O2− obtained with photon energies from 2.033 eV to 3.495 eV exhibit numerous close-lying neutral states with photon-energy-dependent relative intensities. Transitions to states falling within the electron binding energy window of 0.9 and 1.6 eV are attributed to one- or two-electron transitions to the ground and low-lying excited neutral states. An additional, manifold of electronic states observed in the 2.1 to 2.8 eV window cannot be assigned to any simple one-electron transitions. Because of the relatively simple electronic structure from the half-filled 4f7 subshell occupancy in Gd2O2–, the numerous transitions observed in the spectra are fairly well-resolved, allowing a detailed view of the changes in relative intensities of individual transitions with photon energy. With supporting calculations on the numerous close-lying electronic states, we suggest a description of strong photoelectron-valence electron interactions that result in the photon-energy dependent shake-up transitions and switching between ferro- and antiferromagnetic coupling. </p
Overcoming Strain-Induced Rearrangement Reactions: A Mild Dehydrative Aromatization Protocol for Synthesis of Highly Distorted <i>p</i>‑Phenylenes
A series
of <i>p</i>-terphenyl-based macrocycles, containing
highly distorted <i>p</i>-phenylene units, have been synthesized.
Biaryl bonds of the nonplanar <i>p</i>-terphenyl nuclei
were constructed in the absence of Pd-catalyzed or Ni-mediated cross-coupling
reactions, using 1,4-diketones as surrogates to strained arene units.
A streamlined synthetic protocol for the synthesis of 1,4-diketo macrocycles
has been developed, using only 2.5 mol % of the Hoveyda–Grubbs
second-generation catalyst in both metathesis and transfer hydrogenation
reactions. Under protic acid-mediated dehydrative aromatization conditions,
the central and most strained benzene ring of the <i>p</i>-terphenyl systems was susceptible to rearrangement reactions. To
overcome this, a dehydrative aromatization protocol using the Burgess
reagent was developed. Under these conditions, no strain-induced rearrangement
reactions occur, delivering <i>p</i>-phenylene units with
up to 28.4 kcal/mol strain energy and deformation angles that sum
up to 40°