Deterministic Quantum Mechanics: Classical nuclear motion explains chemical reactions and spectra

Is a classical description of nuclear motion sufficient when describing chemical reactions? The present paper investigates some phenomena that were previously attributed to nuclear quantum effects. The aim is to show that these phenomena can be modelled with traditional Car-Parrinello molecular dynamics, that is, with a method which treats nuclear motion classically. We find that no additional paradigm is needed for describing chemical reactions. The special reactivity observed for carbenes can be attributed to the special environment represented by a noble gas matrix. Also the infrared spectrum of porphycene is perfectly modelled by traditional Car-Parrinello molecular dynamics. If no more convincing examples are produced, one will stick to deterministic quantum mechanics, as it is the simpler theory which, in addition, is free of paradoxa.

Controlled ultrafast ππ*-πσ* dynamics in tryptophan-based peptides with tailored micro-environment

Ultrafast charge, energy and structural dynamics in molecules are driven by the topology of the multidimensional potential energy surfaces that determines the coordinated electronic and nuclear motion. These processes are also strongly influenced by the interaction with the molecular environment, making very challenging a general understanding of these dynamics on a microscopic level. Here we use electrospray and mass spectrometry technologies to produce isolated molecular ions with a controlled micro-environment. We measure ultrafast photo-induced ππ*-πσ* dynamics in tryptophan species in the presence of a single, charged adduct. A striking increase of the timescale by more than one order of magnitude is observed when changing the added adduct atom. A model is proposed to rationalize the results, based on the localized and delocalized effects of the adduct on the electronic structure of the molecule. These results offer perspectives to control ultrafast molecular processes by designing the micro-environment on the Angström length scale.

Electronic spin separation induced by nuclear motion near conical intersections

Though the concept of Berry force was proposed thirty years ago, little is known about the practical consequences of this force as far as chemical dynamics are concerned. Here, we report that when molecular dynamics pass near a conical intersection, a massive Berry force can appear as a result of even a small amount of spin-orbit coupling (<10−3 eV), and this Berry force can in turn dramatically change pathway selection. In particular, for a simple radical reaction with two outgoing reaction channels, an exact quantum scattering solution in two dimensions shows that the presence of a significant Berry force can sometimes lead to spin selectivity as large as 100%. Thus, this article opens the door for organic chemists to start designing spintronic devices that use nuclear motion and conical intersections (combined with standard spin-orbit coupling) in order to achieve spin selection. Vice versa, for physical chemists, this article also emphasizes that future semiclassical simulations of intersystem crossing (which have heretofore ignored Berry force) should be corrected to account for the spin polarization that inevitably arises when dynamics pass near conical intersections.

Quantum states of the endohedral fullerene Li+@C60 surrounded by anions: energy decomposition analysis of nuclear wave functions

Lithium is the lightest metal element. To date, little is known about its quantized nuclear motion in nanoscale porous structures.

Fingerprint region of the formic acid dimer: variational vibrational computations in curvilinear coordinates

Curvilinear kinetic energy models are developed for variational nuclear motion computations including the inter- and the low-frequency intra-molecular degrees of freedom of the formic acid dimer. The coupling of the...