206 research outputs found
A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Bicyclic Systems
Pursuing our efforts to define highly-accurate estimates of the relative
energies of excited states in organic molecules, we investigate, with
coupled-cluster methods including iterative triples (CC3 and CCSDT), the
vertical excitation energies of 10 bicyclic molecules (azulene, benzoxadiazole,
benzothiadiazole, diketopyrrolopyrrole, fuofuran, phthalazine, pyrrolopyrrole,
quinoxaline, tetrathiafulvalene, and thienothiophene). In total, we provide
\emph{aug}-cc-pVTZ reference vertical excitation energies for 91 excited states
of these relatively large systems. We use these reference values to benchmark
various wave function methods, i.e., CIS(D), EOM-MP2, CC2, CCSD, STEOM-CCSD,
CCSD(T)(a)*, CCSDR(3), CCSDT-3, ADC(2), ADC(2.5), ADC(3), as well as some
spin-scaled variants of both CC2 and ADC(2). These results are compared to
those obtained previously on smaller molecules. It turns out that while the
accuracy of some methods is almost unaffected by system size, e.g., CIS(D) and
CC3, the performance of others can significantly deteriorate as the systems
grow, e.g., EOM-MP2 and CCSD, whereas others, e.g., ADC(2) and CC2, become more
accurate for larger derivatives.Comment: 19 pages, 2 figure
Assessing the Performances of CASPT2 and NEVPT2 for Vertical Excitation Energies
Methods able to simultaneously account for both static and dynamic electron
correlations have often been employed, not only to model photochemical events,
but also to provide reference values for vertical transition energies, hence
allowing to benchmark lower-order models. In this category, both CASPT2 and
NEVPT2 are certainly popular, the latter presenting the advantage of not
requiring the application of the empirical
ionization-potential-electron-affinity (IPEA) and level shifts. However, the
actual accuracy of these multiconfigurational approaches is not settled yet. In
this context, to assess the performances of these approaches the present work
relies on highly-accurate ( eV) \emph{aug}-cc-pVTZ vertical
transition energies for 284 excited states of diverse character (174 singlet,
110 triplet, 206 valence, 78 Rydberg, 78 , 119 ,
and 9 double excitations) determined in 35 small- to medium-sized organic
molecules containing from three to six non-hydrogen atoms. The CASPT2
calculations are performed with and without IPEA shift and compared to the
partially-contracted (PC) and strongly-contracted (SC) variants of NEVPT2. We
find that both CASPT2 with IPEA shift and PC-NEVPT2 provide fairly reliable
vertical transition energy estimates, with slight overestimations and mean
absolute errors of and eV, respectively. These values are found
to be rather uniform for the various subgroups of transitions. The present work
completes our previous benchmarks focussed on single-reference wave function
methods (\textit{J.~Chem. Theory Comput.} \textbf{14}, 4360 (2018);
\emph{ibid.}, \textbf{16}, 1711 (2020)), hence allowing for a fair comparison
between various families of electronic structure methods. In particular, we
show that ADC(2), CCSD, and CASPT2 deliver similar accuracies for excited
states with a dominant single-excitation character.Comment: 21 pages, 3 figure (supporting information available
Excitation energies from diffusion Monte Carlo using selected Configuration Interaction nodes
Quantum Monte Carlo (QMC) is a stochastic method which has been particularly
successful for ground-state electronic structure calculations but mostly
unexplored for the computation of excited-state energies. Here, we show that,
within a Jastrow-free QMC protocol relying on a deterministic and systematic
construction of nodal surfaces using selected configuration interaction (sCI)
expansions, one is able to obtain accurate excitation energies at the
fixed-node diffusion Monte Carlo (FN-DMC) level. This evidences that the
fixed-node errors in the ground and excited states obtained with sCI wave
functions cancel out to a large extent. Our procedure is tested on two small
organic molecules (water and formaldehyde) for which we report all-electron
FN-DMC calculations. For both the singlet and triplet manifolds, accurate
vertical excitation energies are obtained with relatively compact
multideterminant expansions built with small (typically double-) basis
sets.Comment: 8 pages, 3 figure
Reference Vertical Excitation Energies for Transition Metal Compounds
To enrich and enhance the diversity of the \textsc{quest} database of
highly-accurate excitation energies
[\href{https://doi.org/10.1002/wcms.1517}{V\'eril \textit{et al.},
\textit{WIREs Comput.~Mol.~Sci.}~\textbf{11}, e1517 (2021)}], we report
vertical transition energies in transition metal compounds. Eleven diatomic
molecules with singlet or doublet ground state containing a fourth-row
transition metal (\ce{CuCl}, \ce{CuF}, \ce{CuH}, \ce{ScF}, \ce{ScH}, \ce{ScO},
\ce{ScS}, \ce{TiN}, \ce{ZnH}, \ce{ZnO}, and \ce{ZnS}) are considered and the
corresponding excitation energies are computed using high-level coupled-cluster
(CC) methods, namely CC3, CCSDT, CC4, and CCSDTQ, as well as
multiconfigurational methods such as CASPT2 and NEVPT2. In some cases, to
provide more comprehensive benchmark data, we also provide full configuration
interaction estimates computed with the \textit{"Configuration Interaction
using a Perturbative Selection made Iteratively"} (CIPSI) method. Based on
these calculations, theoretical best estimates of the transition energies are
established in both the aug-cc-pVDZ and aug-cc-pVTZ basis sets. This allows us
to accurately assess the performance of CC and multiconfigurational methods for
this specific set of challenging transitions. Furthermore, comparisons with
experimental data and previous theoretical results are also reported.Comment: 17 pages, 3 figure
Ground- and Excited-State Dipole Moments and Oscillator Strengths of Full Configuration Interaction Quality
We report ground- and excited-state dipole moments and oscillator strengths
(computed in different ``gauges'' or representations) of full configuration
interaction (FCI) quality using the selected configuration interaction method
known as \textit{Configuration Interaction using a Perturbative Selection made
Iteratively} (CIPSI). Thanks to a set encompassing 35 ground- and excited-state
properties computed in 11 small molecules, the present near-FCI estimates allow
us to assess the accuracy of high-order coupled-cluster (CC) calculations
including up to quadruple excitations. In particular, we show that incrementing
the excitation degree of the CC expansion (from CCSD to CCSDT or from CCSDT to
CCSDTQ) reduces the average error with respect to the near-FCI reference values
by approximately one order of magnitude.Comment: 14 pages, 8 figures (supporting information available
New genetic loci implicated in fasting glucose homeostasis and their impact on type 2 diabetes risk.
Levels of circulating glucose are tightly regulated. To identify new loci influencing glycemic traits, we performed meta-analyses of 21 genome-wide association studies informative for fasting glucose, fasting insulin and indices of beta-cell function (HOMA-B) and insulin resistance (HOMA-IR) in up to 46,186 nondiabetic participants. Follow-up of 25 loci in up to 76,558 additional subjects identified 16 loci associated with fasting glucose and HOMA-B and two loci associated with fasting insulin and HOMA-IR. These include nine loci newly associated with fasting glucose (in or near ADCY5, MADD, ADRA2A, CRY2, FADS1, GLIS3, SLC2A2, PROX1 and C2CD4B) and one influencing fasting insulin and HOMA-IR (near IGF1). We also demonstrated association of ADCY5, PROX1, GCK, GCKR and DGKB-TMEM195 with type 2 diabetes. Within these loci, likely biological candidate genes influence signal transduction, cell proliferation, development, glucose-sensing and circadian regulation. Our results demonstrate that genetic studies of glycemic traits can identify type 2 diabetes risk loci, as well as loci containing gene variants that are associated with a modest elevation in glucose levels but are not associated with overt diabetes
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Smoking-by-genotype interaction in type 2 diabetes risk and fasting glucose.
Smoking is a potentially causal behavioral risk factor for type 2 diabetes (T2D), but not all smokers develop T2D. It is unknown whether genetic factors partially explain this variation. We performed genome-environment-wide interaction studies to identify loci exhibiting potential interaction with baseline smoking status (ever vs. never) on incident T2D and fasting glucose (FG). Analyses were performed in participants of European (EA) and African ancestry (AA) separately. Discovery analyses were conducted using genotype data from the 50,000-single-nucleotide polymorphism (SNP) ITMAT-Broad-CARe (IBC) array in 5 cohorts from from the Candidate Gene Association Resource Consortium (n = 23,189). Replication was performed in up to 16 studies from the Cohorts for Heart Aging Research in Genomic Epidemiology Consortium (n = 74,584). In meta-analysis of discovery and replication estimates, 5 SNPs met at least one criterion for potential interaction with smoking on incident T2D at p<1x10-7 (adjusted for multiple hypothesis-testing with the IBC array). Two SNPs had significant joint effects in the overall model and significant main effects only in one smoking stratum: rs140637 (FBN1) in AA individuals had a significant main effect only among smokers, and rs1444261 (closest gene C2orf63) in EA individuals had a significant main effect only among nonsmokers. Three additional SNPs were identified as having potential interaction by exhibiting a significant main effects only in smokers: rs1801232 (CUBN) in AA individuals, rs12243326 (TCF7L2) in EA individuals, and rs4132670 (TCF7L2) in EA individuals. No SNP met significance for potential interaction with smoking on baseline FG. The identification of these loci provides evidence for genetic interactions with smoking exposure that may explain some of the heterogeneity in the association between smoking and T2D
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Genome-Wide Association Identifies Nine Common Variants Associated With Fasting Proinsulin Levels and Provides New Insights Into the Pathophysiology of Type 2 Diabetes
OBJECTIVE: Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS: We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS: Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10−8). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10−4), improved β-cell function (P = 1.1 × 10−5), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10−6). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS: We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis
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