Ensemble first-principles molecular dynamics simulations of water using the SCAN meta-GGA density functional.

We present an ensemble of 16 independent first-principles molecular dynamics simulations of water performed using the Strongly Constrained and Appropriately Normed (SCAN) meta-generalized gradient approximation exchange-correlation functional. These simulations were used to compute the structural and electronic properties of liquid water, as well as polarizabilities, Raman and infrared spectra. Overall, we find that the SCAN functional used at a simulation temperature of 330 K provides an accurate description of the structural and electronic properties of water while incurring a moderate computational cost.

Quantum cutting using organic molecules.

A methodology is presented in which a combination of quantum electrodynamics, time-dependent perturbation theory, and computational electronic structure analysis allow the prospect for organic quantum cutting to be quantitatively examined from first principles. The internal quantum yield of quantum cutting is ultimately expressed in terms of rate equations that account for all relevant processes. These are populated with excited state properties found using time-dependent density functional theory and configuration interaction methods.

Experimental demonstration of photon upconversion via cooperative energy pooling.

Photon upconversion is a fundamental interaction of light and matter that has applications in fields ranging from bioimaging to microfabrication. However, all photon upconversion methods demonstrated thus far involve challenging aspects, including requirements of high excitation intensities, degradation in ambient air, requirements of exotic materials or phases, or involvement of inherent energy loss processes. Here we experimentally demonstrate a mechanism of photon upconversion in a thin film, binary mixture of organic chromophores that provides a pathway to overcoming the aforementioned disadvantages.

Energy pooling upconversion in organic molecular systems.

A combination of molecular quantum electrodynamics, perturbation theory, and ab initio calculations was used to create a computational methodology capable of estimating the rate of three-body singlet upconversion in organic molecular assemblies. The approach was applied to quantify the conditions under which such relaxation rates, known as energy pooling, become meaningful for two test systems, stilbene-fluorescein and hexabenzocoronene-oligothiophene. Both exhibit low intramolecular conversion, but intermolecular configurations exist in which pooling efficiency is at least 90% when placed in competition with more conventional relaxation pathways.