2 research outputs found
Molecular Screening for Terahertz Detection with Machine-Learning-Based Methods
The molecular requirements are explored for achieving efficient signal up-conversion in a recently
developed technique for terahertz (THz) detection based on molecular optomechanics. We discuss which
molecular and spectroscopic properties are most important for predicting efficient THz detection and
outline a computational approach based on quantum-chemistry and machine-learning methods for
calculating these properties. We validate this approach by bulk and surface-enhanced Raman scattering
and infrared absorption measurements. We develop a virtual screening methodology performed on
databases of millions of commercially available compounds. Quantum-chemistry calculations for about
3000 compounds are complemented by machine-learning methods to predict applicability of 93 000
organic molecules for detection. Training is performed on vibrational spectroscopic properties based on
absorption and Raman scattering intensities. Our top molecules have conversion intensity two orders of
magnitude higher than an average molecule from the database. We also discuss how other properties like
molecular shape and self-assembling properties influence the detection efficiency. We identify molecular
moieties whose presence in the molecules indicates high activity for THz detection and show an example
where a simple modification of a frequently used self-assembling compound can enhance activity 85-fold.
The capabilities of our screening method are demonstrated on narrow-band and broadband detection
examples, and its possible applications in surface-enhanced spectroscopy are also discussed
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