3,894 research outputs found
First principles view on chemical compound space: Gaining rigorous atomistic control of molecular properties
A well-defined notion of chemical compound space (CCS) is essential for
gaining rigorous control of properties through variation of elemental
composition and atomic configurations. Here, we review an atomistic first
principles perspective on CCS. First, CCS is discussed in terms of variational
nuclear charges in the context of conceptual density functional and molecular
grand-canonical ensemble theory. Thereafter, we revisit the notion of compound
pairs, related to each other via "alchemical" interpolations involving
fractional nuclear chargens in the electronic Hamiltonian. We address Taylor
expansions in CCS, property non-linearity, improved predictions using reference
compound pairs, and the ounce-of-gold prize challenge to linearize CCS.
Finally, we turn to machine learning of analytical structure property
relationships in CCS. These relationships correspond to inferred, rather than
derived through variational principle, solutions of the electronic
Schr\"odinger equation
Many Molecular Properties from One Kernel in Chemical Space
We introduce property-independent kernels for machine learning modeling of
arbitrarily many molecular properties. The kernels encode molecular structures
for training sets of varying size, as well as similarity measures sufficiently
diffuse in chemical space to sample over all training molecules. Corresponding
molecular reference properties provided, they enable the instantaneous
generation of ML models which can systematically be improved through the
addition of more data. This idea is exemplified for single kernel based
modeling of internal energy, enthalpy, free energy, heat capacity,
polarizability, electronic spread, zero-point vibrational energy, energies of
frontier orbitals, HOMO-LUMO gap, and the highest fundamental vibrational
wavenumber. Models of these properties are trained and tested using 112 kilo
organic molecules of similar size. Resulting models are discussed as well as
the kernels' use for generating and using other property models
Modeling Electronic Quantum Transport with Machine Learning
We present a Machine Learning approach to solve electronic quantum transport
equations of one-dimensional nanostructures. The transmission coefficients of
disordered systems were computed to provide training and test datasets to the
machine. The system's representation encodes energetic as well as geometrical
information to characterize similarities between disordered configurations,
while the Euclidean norm is used as a measure of similarity. Errors for
out-of-sample predictions systematically decrease with training set size,
enabling the accurate and fast prediction of new transmission coefficients. The
remarkable performance of our model to capture the complexity of interference
phenomena lends further support to its viability in dealing with transport
problems of undulatory nature.Comment: 5 pages, 4 figure
Why Managers Hold Shares of Their Firms: An Empirical Analysis
We examine the relationship between CEO ownership and stock market performance. Firms in which the CEO voluntarily holds a considerable share of outstanding stocks outperform the market by more than 10% p.a. after controlling for traditional risk factors. The effect is most pronounced in firms that are characterized by large managerial discretion of the CEO. The abnormal returns we document are one potential explanation why so many CEOs hold a large fraction of their own company’s stocks. We also examine several potential explanations why the existence of an owner CEO is not fully reflected in prices but leads to abnormal returns.CEO-Ownership, Asset Pricing with large shareholders.
Quantum Mechanical Treatment of Variable Molecular Composition: From "Alchemical" Changes of State Functions to Rational Compound Design
"Alchemical" interpolation paths, i.e.~coupling systems along fictitious
paths that without realistic correspondence, are frequently used within
materials and molecular modeling and simulation protocols for the estimation of
relative changes in state functions such as free energies. We discuss
alchemical changes in the context of quantum chemistry, and present
illustrative numerical results for the changes of HOMO eigenvalues of the He
atom due to a linear alchemical teleportation---the simultaneous annihilation
and creation of nuclear charges at different locations. To demonstrate the
predictive power of alchemical first order derivatives (Hellmann-Feynman) the
covalent bond potential of hydrogen fluoride and hydrogen chloride is
investigated, as well as the van-der-Waals binding in the water-water and
water-hydrogen fluoride dimer, respectively. Based on converged electron
densities for one configuration, the versatility of alchemical derivatives is
exemplified for the screening of entire binding potentials with reasonable
accuracy. Finally, we discuss constraints for the identification of non-linear
coupling potentials for which the energy's Hellmann-Feynman derivative will
yield accurate predictions
Transferable atomic multipole machine learning models for small organic molecules
Accurate representation of the molecular electrostatic potential, which is
often expanded in distributed multipole moments, is crucial for an efficient
evaluation of intermolecular interactions. Here we introduce a machine learning
model for multipole coefficients of atom types H, C, O, N, S, F, and Cl in any
molecular conformation. The model is trained on quantum chemical results for
atoms in varying chemical environments drawn from thousands of organic
molecules. Multipoles in systems with neutral, cationic, and anionic molecular
charge states are treated with individual models. The models' predictive
accuracy and applicability are illustrated by evaluating intermolecular
interaction energies of nearly 1,000 dimers and the cohesive energy of the
benzene crystal.Comment: 11 pages, 6 figure
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