1,720,973 research outputs found
Basis Set Incompleteness Errors in Fixed-Node Diffusion Monte Carlo Calculations on Noncovalent Interactions
No full textBasis set incompleteness error (BSIE) is a common
source of error in quantum chemistry calculations, but it has not
been comprehensively studied in fixed-node Diffusion Monte Carlo
(FN-DMC) calculations. FN-DMC, being a projection method, is
often considered minimally affected by basis set biases. Here, we
show that this assumption is not always valid. While the relative
error introduced by a small basis set in the total FN-DMC energy is
minor, it can become significant in binding energy (Eb) evaluations
of weakly interacting systems. We systematically investigated BSIEs
in FN-DMC-based Eb evaluations using the A24 data set, a well-
known benchmark set of 24 noncovalently bound dimers. We found
that BSIEs in FN-DMC evaluations of Eb are indeed significant
when small localized basis sets, such as cc-pVDZ and cc-pVTZ, are
employed. Our study shows that the aug-cc-pVTZ basis set family strikes a good balance between computational cost and BSIEs in
the Eb calculations. We also found that augmenting the basis sets with diffuse orbitals, using counterpoise correction, or both,
effectively mitigates BSIEs, allowing smaller basis sets such as
aug-cc-pVDZ to be used
Systematic discrepancies between reference methods for noncovalent interactions within the S66 dataset
No full textThe accurate treatment of noncovalent interactions is necessary to model a wide range of applications, from molecular crystals to surface catalysts to aqueous solutions and many more. Quantum diffusion Monte Carlo (DMC) and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)] are considered two widely trusted methods for treating noncovalent interactions. However, while they have been well-validated for small molecules, recent work has indicated that these two methods can disagree by more than 7.5 kcal/mol for larger systems. The origin of this discrepancy remains unknown. Moreover, the lack of systematic comparisons, particularly for medium-sized complexes, has made it difficult to identify which systems may be prone to such disagreements and the potential scale of these differences. In this work, we leverage the latest developments in DMC to compute interaction energies for the entire S66 dataset, containing 66 medium-sized complexes with a balanced representation of dispersion and electrostatic interactions. Comparison to previous CCSD(T) references reveals systematic trends, with DMC predicting stronger binding than CCSD(T) for electrostatic-dominated systems, while the binding becomes weaker for dispersion-dominated systems. We show that the relative strength of this discrepancy is correlated to the ratio of electrostatic and dispersion interactions, as obtained from energy decomposition analysis methods. Finally, we have pinpointed model systems: the hydrogen-bonded acetic acid dimer (ID 20) and dispersion-dominated uracil–cyclopentane dimer (ID 42), where these discrepancies are particularly prominent. These systems offer cost-effective benchmarks to guide future developments in DMC, CCSD(T), as well as the wider electronic structure theory community
Cooperative CO2 capture via oxalate formation on metal-decorated graphene
No full textCO2 capture using carbon-based materials, particularly graphene and graphene-like materials, is a promising strategy to deal with CO2 emissions. However, significant gaps remain in our understanding of the molecular-level interaction between CO2 molecules and graphene, particularly in terms of chemical bonding and electron transfer. In this work, we employ random structure search and density functional theory to understand the adsorption of CO2 molecules on Ca-, Sr-, Na-, K-, and Ti-decorated graphene surfaces. Compared to the pristine material, we observe enhanced CO2 adsorption on the decorated graphene surfaces. Particularly on group 2 metals and titanium-decorated graphene, CO2 can be strongly chemisorbed as a bent CO2 anion or as an oxalate, depending on the number of CO2 molecules. Electronic structure analysis reveals that the adsorption mechanism involves a charge transfer from the metal adatom to the adsorbed CO2. Overall, this study suggests that reducing CO2 to oxalate on group 2 metals and titanium-decorated graphene surfaces is a potential strategy for CO2 storage
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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