1,403 research outputs found
Alchemical normal modes unify chemical space
In silico design of new molecules and materials with desirable quantum
properties by high-throughput screening is a major challenge due to the high
dimensionality of chemical space. To facilitate its navigation, we present a
unification of coordinate and composition space in terms of alchemical normal
modes (ANMs) which result from second order perturbation theory. ANMs assume a
predominantly smooth nature of chemical space and form a basis in which new
compounds can be expanded and identified. We showcase the use of ANMs for the
energetics of the iso-electronic series of diatomics with 14 electrons, BN
doped benzene derivatives (C(BN)H with ),
predictions for over 1.8 million BN doped coronene derivatives, and genetic
energy optimizations in the entire BN doped coronene space. Using Ge lattice
scans as reference, the applicability ANMs across the periodic table is
demonstrated for III-V and IV-IV-semiconductors Si, Sn, SiGe, SnGe, SiSn, as
well as AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb. Analysis of our
results indicates simple qualitative structure property rules for estimating
energetic rankings among isomers. Useful quantitative estimates can also be
obtained when few atoms are changed to neighboring or lower lying elements in
the periodic table. The quality of the predictions often increases with the
symmetry of system chosen as reference due to cancellation of odd order terms.
Rooted in perturbation theory the ANM approach promises to generally enable
unbiased compound exploration campaigns at reduced computational cost
Ab initio molecular dynamics calculations of ion hydration free energies
We apply ab initio molecular dynamics (AIMD) methods in conjunction with the
thermodynamic integration or "lambda-path" technique to compute the intrinsic
hydration free energies of Li+, Cl-, and Ag+ ions. Using the
Perdew-Burke-Ernzerhof functional, adapting methods developed for classical
force field applications, and with consistent assumptions about surface
potential (phi) contributions, we obtain absolute AIMD hydration free energies
(Delta G(hyd)) within a few kcal/mol, or better than 4%, of Tissandier 's [J.
Phys. Chem. A 102, 7787 (1998)] experimental values augmented with the SPC/E
water model phi predictions. The sums of Li+/Cl- and Ag+/Cl- AIMD Delta G(hyd),
which are not affected by surface potentials, are within 2.6% and 1.2 % of
experimental values, respectively. We also report the free energy changes
associated with the transition metal ion redox reaction Ag++Ni+-> Ag+Ni2+ in
water. The predictions for this reaction suggest that existing estimates of
Delta G(hyd) for unstable radiolysis intermediates such as Ni+ may need to be
extensively revised.Comment: 18 pages, 8 figures. This version is essentially the one published in
J. Chem. Phy
Ontologies, Mental Disorders and Prototypes
As it emerged from philosophical analyses and cognitive research, most concepts exhibit typicality effects, and resist to the efforts of defining them in terms of necessary and sufficient conditions. This holds also in the case of many medical concepts. This is a problem for the design of computer science ontologies, since knowledge representation formalisms commonly adopted in this field do not allow for the representation of concepts in terms of typical traits. However, the need of representing concepts in terms of typical traits concerns almost every domain of real world knowledge, including medical domains. In particular, in this article we take into account the domain of mental disorders, starting from the DSM-5 descriptions of some specific mental disorders. On this respect, we favor a hybrid approach to the representation of psychiatric concepts, in which ontology oriented formalisms are combined to a geometric representation of knowledge based on conceptual spaces
Prediction of the Atomization Energy of Molecules Using Coulomb Matrix and Atomic Composition in a Bayesian Regularized Neural Networks
Exact calculation of electronic properties of molecules is a fundamental step
for intelligent and rational compounds and materials design. The intrinsically
graph-like and non-vectorial nature of molecular data generates a unique and
challenging machine learning problem. In this paper we embrace a learning from
scratch approach where the quantum mechanical electronic properties of
molecules are predicted directly from the raw molecular geometry, similar to
some recent works. But, unlike these previous endeavors, our study suggests a
benefit from combining molecular geometry embedded in the Coulomb matrix with
the atomic composition of molecules. Using the new combined features in a
Bayesian regularized neural networks, our results improve well-known results
from the literature on the QM7 dataset from a mean absolute error of 3.51
kcal/mol down to 3.0 kcal/mol.Comment: Under review ICANN 201
The Privatization Origins of Political Corporations: Evidence from the Pinochet Regime
We show that the sale of state owned firms in dictatorships can help political corporations to emerge and persist over time. Using new data, we characterize Pinochet’s privatizations in Chile and find that some firms were sold underpriced to politically connected buyers. These newly private firms benefited financially from the Pinochet regime. Once democracy arrived, they formed connections with the new government, financed political campaigns, and were more likely to appear in the Panama Papers. These findings reveal how dictatorships can influence young democracies using privatization reforms
Self-reported psychopathy in the Middle East: a cross-national comparison across Egypt, Saudi Arabia, and the United States
Background: The construct of psychopathy is sparsely researched in the non-Western world, particularly in the Middle East. As such, the extent to which the psychopathy construct can be generalized to other cultures, including Middle Eastern Arab cultures, is largely unknown. Methods: The present study investigated the cross-cultural/national comparability of self-reported psychopathy in the United States (N = 786), Egypt (N = 296), and Saudi Arabia (N = 341). Results: A widely used psychopathy questionnaire demonstrated largely similar properties across the American and Middle Eastern samples and associations between Five Factor Model (FFM) personality and psychopathy were broadly consistent. Nevertheless, several notable cross-cultural differences emerged, particularly with regard to the internal consistencies of psychopathy dimensions and the correlates of Coldheartedness. Additionally, in contrast to most findings in Western cultures, associations between psychopathy and FFM personality varied consistently by gender in the Egyptian sample. Conclusions: These findings lend preliminary support to the construct validity of self-reported psychopathy in Arabic-speaking cultures, providing provisional evidence for the cross-cultural generalizability of certain core characteristics of psychopathy
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