10 research outputs found
Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design
Resilience of benthic deep-sea fauna to mining activities
With increasing demand for mineral resources, extraction of polymetallic sulphides at hydrothermal vents, cobalt-rich ferromanganese crusts at seamounts, and polymetallic nodules on abyssal plains may be imminent. Here, we shortly introduce ecosystem characteristics of mining areas, report on recent mining developments, and identify potential stress and disturbances created by mining. We analyze species' potential resistance to future mining and perform meta-analyses on population density and diversity recovery after disturbances most similar to mining: volcanic eruptions at vents, fisheries on seamounts, and experiments that mimic nodule mining on abyssal plains. We report wide variation in recovery rates among taxa, size, and mobility of fauna. While densities and diversities of some taxa can recover to or even exceed pre-disturbance levels, community composition remains affected after decades. The loss of hard substrata or alteration of substrata composition may cause substantial community shifts that persist over geological timescales at mined sites. (C) 2017 Elsevier Ltd. All rights reserved.European Union Seventh Framework Programme (FP7) under the MIDAS project; FCT [IF/00029/2014/CP1230/CT0002, SFRH/ BPD/110278/2015]; Spanish RTD project NUREIEV [CTM2013-44598-R]; Ministry of Economy and Competitiveness [SGR 1068]; Generalitat de Catalunya autonomous government; European Union Horizon research and innovation programme [689518]; Fundacao para a Ciencia e a Tecnologia [UID/MAR/04292/2013]; German Ministry of Research (BMBF) [03F0707A-G]; Program Investigador FCT [IF/01194/2013/CP1199/CT0002]info:eu-repo/semantics/publishedVersio
Universal Exciton Size in Organic Polymers is Determined by Nonlocal Orbital Exchange in Time-Dependent Density Functional Theory
The exciton size
of the lowest singlet excited state in a diverse
set of organic π-conjugated polymers is studied and found to
be a universal, system-independent quantity of approximately 7 Å
in the single-chain picture. With time-dependent density functional
theory (TDDFT), its value as well as the overall description of the
exciton is almost exclusively governed by the amount of nonlocal orbital
exchange. This is traced back to the lack of the Coulomb attraction
between the electron and hole quasiparticles in pure TDDFT, which
is reintroduced only with the admixture of nonlocal orbital exchange
Detailed Wave Function Analysis for Multireference Methods: Implementation in the Molcas Program Package and Applications to Tetracene
High-level
multireference computations on electronically excited
and charged states of tetracene are performed, and the results are
analyzed using an extensive wave function analysis toolbox that has
been newly implemented in the Molcas program package. Aside
from verifying the strong effect of dynamic correlation, this study
reveals an unexpected critical influence of the atomic orbital basis
set. It is shown that different polarized double-ζ basis sets
produce significantly different results for energies, densities, and
overall wave functions, with the best performance obtained for the
atomic natural orbital (ANO) basis set by Pierloot et al. Strikingly,
the ANO basis set not only reproduces the energies but also performs
exceptionally well in terms of describing the diffuseness of the different
states and of their attachment/detachment densities. This study, thus,
not only underlines the fact that diffuse basis functions are needed
for an accurate description of the electronic wave functions but also
shows that, at least for the present example, it is enough to include
them implicitly in the contraction scheme
Benchmarking Excited-State Calculations Using Exciton Properties
Benchmarking is an every-day task
in computational chemistry, yet
making meaningful comparisons between different methods is nontrivial.
Benchmark studies often focus on the most obvious quantities such
as energy differences. But to gain insight, it is desirable to explain
the discrepancies between theoretical methods in terms of underlying
wave functions and, consequently, physically relevant quantities.
We present a new strategy of benchmarking excited-state calculations,
which goes beyond excitation energies and oscillator strengths and
involves the analysis of exciton properties based on the one-particle
transition density matrix. By using this approach, we compare the
performance of many-body excited-state methods (equation-of-motion
coupled-cluster and algebraic diagrammatic construction) and time-dependent
density functional theory. The selected examples illustrate the utility
of different exciton descriptors in assigning state character and
explaining the discrepancies among different methods. The examples
include Rydberg, valence, and charge-transfer states, as well as delocalized
excitonic states in large conjugated systems and states with substantial
doubly excited character
OpenMolcas: From Source Code to Insight
10.1021/acs.jctc.9b00532JOURNAL OF CHEMICAL THEORY AND COMPUTATION15115925-596
OpenMolcas : From Source Code to Insight
In this Article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations include an array of additional options and functionalities. The paper proceeds and describes developments related to explorations of potential energy surfaces. Here we present methods for the optimization of conical intersections, the simulation of adiabatic and nonadiabatic molecular dynamics, and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the Article describes features unique to simulations of spectroscopic and magnetic phenomena such as the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism, and properties. Finally, the paper describes a number of built-in and add-on features to support the OpenMolcas platform with postcalculation analysis and visualization, a multiscale simulation option using frozen-density embedding theory, and new electronic and muonic basis sets
OpenMolcas: From source code to insight
In this article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already
includes a large number of new developments realized during the transition from
the commercial MOLCAS product to the open-source platform. The paper initially
describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features
of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density
matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations
include an array of additional options and functionalities. The paper proceeds and
describes developments related to explorations of potential energy surfaces. Here
we present methods for the optimization of conical intersections, the simulation of
adiabatic and nonadiabatic molecular dynamics and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the article describes
features unique to simulations of spectroscopic and magnetic phenomena such as
the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism and properties. Finally, the paper
describes a number of built-in and add-on features to support the OpenMolcas platform with post calculation analysis and visualization, a multiscale simulation option
using frozen-density embedding theory and new electronic and muonic basis sets
Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design