: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The theorems at the core of density functional theory (DFT) state that the energy of a many-electron system in its ground state is fully defined by its electron density distribution. This connection is made via the exact functional for the energy, which minimizes at the exact density. For years, DFT development focused on energies, implicitly assuming that functionals producing better energies become better approximations of the exact functional. We examined the other side of the coin: the energy-minimizing electron densities for atomic species, as produced by 128 historical and modern DFT functionals. We found that these densities became closer to the exact ones, reflecting theoretical advances, until the early 2000s, when this trend was reversed by unconstrained functionals sacrificing physical rigor for the flexibility of empirical fitting.

https://science.sciencemag.org/content/sci/355/6320/49.full.pdf

Density functional theory is straying from the path toward the exact functional.

The use of a PtAu catalyst as an anode catalyst for the oxidation of formic acid in direct formic acid fuel cells is described. Catalytic activities of PtAu and PtRu anodes were studied using a linear sweep voltammetry technique in a single cell configuration. PtAu showed a lower on-set potential and a larger current density than that of PtRu in formic acid oxidation. In addition, the maximum power densities at 30 ◦ C for PtAu and PtRu were 94 and 74 mW cm −2 , respectively. In order to evaluate long-term durability, the single cells were operated for hundreds of hours with a 6 M aqueous formic acid solution at 60 ◦ C under 100 mA cm −2 . The difference in performance between PtAu and PtRu after 500 h reached ca.

Short communication Electro-oxidation of methanol and formic acid on PtRu and PtAu for direct liquid fuel cells

Magnetic freezing is nowadays established as a commercial reality mainly oriented towards the food market. According to advertisements, magnetic freezing is able to generate tiny ice crystals throughout the frozen product, prevent cell destruction, and preserve the quality of fresh food intact after thawing. If all these advantages were true, magnetic freezing would represent a significant advance in freezing technology, not only for food preservation, but also for cryopreservation of biological specimens such as cells, tissues, and organs. Magnetic fields (MFs) are supposed to act directly on water by orientating, vibrating, and/or spinning molecules to prevent them from clustering and, thus, to promote supercooling. However, many doubts exist about the real effects of MFs on freezing and the science behind the potential mechanisms involved. To provide a basis for extending the understanding of magnetic freezing, this paper presents a critical review of the materials published in the literature up to now, including both patents and experimental results. After examining the information available, it was not possible to discern whether MFs have an appreciable effect on supercooling, freezing kinetics, ice crystals, quality, and/or viability of the frozen products. Experiments described in the literature frequently fail to identify and/or control all the factors that can play a role in magnetic freezing. Moreover, many of the comparisons between magnetic and conventional freezing are not correctly designed to draw valid conclusions, and wide ranges of MF intensities and frequencies are unexplored. Therefore, more rigorous experimentation and further evidence are needed to confirm or reject the efficacy of MFs in improving the quality of frozen products.

/pdf/effects-of-magnetic-fields-on-freezing-application-to-3hivtckagq.pdf

Effects of Magnetic Fields on Freezing: Application to Biological Products.

The properties of water confined inside nanotubes are of considerable scientific and technological interest. We use molecular dynamics to investigate the structure and average orientation of water flowing within a carbon nanotube. We find that water exhibits biaxial paranematic liquid crystal ordering both within the nanotube and close to its ends. This preferred molecular ordering is enhanced when an axial electric field is applied, affecting the water flow rate through the nanotube. A spatially patterned electric field can minimize nanotube entrance effects and significantly increase the flow rate.

/pdf/electric-fields-can-control-the-transport-of-water-in-carbon-3a571t2ooc.pdf

Electric fields can control the transport of water in carbon nanotubes

An improved B3LYP method in the calculation of organic thermochemistry and reactivity

Formic acid was used as the model of lauric acid to investigate the microscopic mechanism of the anti-icing behavior and was checked to find out if it can be catalyzed to produce H2 for fuel cells by the α-Al2O3(0001) 2 × 2 supercell slab model. The density functional theory with the all-electron double numerical polarized basis sets was employed. The results show that when it involves the carboxyl O and hydroxyl H atom the 1,2-dissociated adsorbate is the most stable intermediate on the dry Al2O3(0001) surface and is energetic barrier free to form the fairly stable ROCO- and HO-covered surface with the binding energy of 59.5 kcal/mol, and this dissociation mode has the lowest energy barrier of 14.9 kcal/mol to form the HOCO- and H2O-covered surface after the surface is fully hydroxylated. The energetic barrier of the HCOOH dehydrogenation and dehydration reactions on the alumina surface decreased considerably from 65.3 to 30.6 kcal/mol and from 62.1 to 26.8 kcal/mol, respectively, in comparison with the ...

Theoretical Study of the Adsorption/Dissociation Reactions of Formic Acid on the α-Al2O3(0001) Surface

TIP4P/2005 force-field-based classical molecular dynamics simulations were employed to investigate the microscopic mechanism for the ice growth from supercooled water when the external electric (0–109 V/m) and magnetic fields (0–10 T) are applied simultaneously. Using the direct coexistence ice/water interface, the anisotropic effect of electric and magnetic fields on the basal, primary prismatic, and the secondary prismatic planes of ice Ih has been calculated. It was revealed for the first time that the solvation shells of supercooled water could be affected by the cooperative electric and magnetic fields. Meanwhile, the self-diffusion coefficient is lowered, and the shear viscosity increases considerably. The critical electric and magnetic fields to accelerate ice growth on the prismatic plane are fairly low (ca. 106 V/m and 0.01 T). In contrast, the basal plane is hardly affected unless the fields increase to the order 109 V/m and 10 T. Rotational dynamics of water molecules might play an important ro...

Hua Hou

Papers

An improved B3LYP method in the calculation of organic thermochemistry and reactivity

Theoretical Study of the Adsorption/Dissociation Reactions of Formic Acid on the α-Al2O3(0001) Surface

Molecular Dynamics Simulations of Ice Growth from Supercooled Water When Both Electric and Magnetic Fields Are Applied

H proton intramolecular transformation in OH-OO-isoprene radicals