Correlated quantum-chemical methods for condensed matter systems, such as the random phase approximation (RPA), hold the promise of reaching a level of accuracy much higher than that of conventional density functional theory approaches. However, the high computational cost of such methods hinders their broad applicability, in particular for finite-temperature molecular dynamics simulations. We propose a method that couples machine learning techniques with thermodynamic perturbation theory to estimate finite-temperature properties using correlated approximations. We apply this approach to compute the enthalpies of adsorption in zeolites and show that reliable estimates can be obtained by training a machine learning model with as few as 10 RPA energies. This approach paves the way to the broader use of computationally expensive quantum-chemical methods to predict the finite-temperature properties of condensed matter systems.

As nanocrystals (NCs) gain maturity, they become central building blocks for optoelectronics in devices such as solar cells and, more recently, infrared focal plane arrays. Now that proof of concept...

Quantum confinement opens a large energy gap E g in HgTe nanocrystals (NCs), which is a non-trivial semi-metal (E g bulk < 0) in the bulk crystal limit. In this context, we present a theoretical study of the evolution of the dielectric and optical properties of HgTe from bulk material to isolated NCs up to compact films of NCs. In the latter case, we compare the calculated complex dielectric constant with the one measured by broadband ellipsometry on synthesized colloidal NC film. The theoryexperiment agreement is excellent, demonstrating the interest of simulations based on tight-binding calculations combined with a Bruggeman-type effective medium model to predict the optical properties of HgTe NC layers. Our calculations also reveal that the complex dielectric constant ε NC (ω) of isolated NCs differs considerably from that of bulk HgTe and depends strongly on their size, especially for the real part. This variation results only from surface effects for energies ℏω≪E g . This behavior is identical to that of NCs from semiconductors such as Si, InAs, or CdTe. On the other hand, we reveal the existence of an important variation of ε NC (ω) of another nature; when going from a normal semiconductor (E g > 0) to a semi-metal (E g bulk < 0), the material undergoes a transition of topological nature that we predict for a NC diameter of ∼26 nm.