DFT Modelling of Molecular Structure, Vibrational and UV-Vis Absorption Spectra of T-2 Toxin and 3-Deacetylcalonectrin

This paper discusses the applicability of optical and vibrational spectroscopies for the identification and characterization of the T-2 mycotoxin. Vibrational states and electronic structure of the T-2 toxin molecules are simulated using a density-functional quantum-mechanical approach. A numerical experiment aimed at comparing the predicted structural, vibrational and electronic properties of the T-2 toxin with analogous characteristics of the structurally similar 3-deacetylcalonectrin is performed, and the characteristic spectral features that can be used as fingerprints of the T-2 toxin are determined. It is shown that theoretical studies of the structure and spectroscopic features of trichothecene molecules facilitate the development of methods for the detection and characterization of the metabolites.

Observation of a gravitational Aharonov-Bohm effect

Gravitational interference The Aharonov-Bohm effect is a quantum mechanical effect in which a magnetic field affects the phase of an electron wave as it propagates along a wire. Atom interferometry exploits the wave characteristic of atoms to measure tiny differences in phase as they take different paths through the arms of an interferometer. Overstreet et al . split a cloud of cold rubidium atoms into two atomic wave packets about 25 centimeters apart and subjected one of the wave packets to gravitational interaction with a large mass (see the Perspective by Roura). The authors state that the observed phase shift is consistent with a gravitational Aharonov-Bohm effect. —ISO

Stochastic emulation of quantum algorithms

Quantum algorithms profit from the interference of quantum states in an exponentially large Hilbert space and the fact that unitary transformations on that Hilbert space can be broken down to universal gates that act only on one or two qubits at the same time. The former aspect renders the direct classical simulation of quantum algorithms difficult. Here we introduce higher-order partial derivatives of a probability distribution of particle positions as a new object that shares these basic properties of quantum mechanical states needed for a quantum algorithm. Discretization of the positions allows one to represent the quantum mechanical state of $\nb$ qubits by $2(\nb+1)$ classical stochastic bits. Based on this, we demonstrate many-particle interference and representation of pure entangled quantum states via derivatives of probability distributions and find the universal set of stochastic maps that correspond to the quantum gates in a universal gate set. We prove that the propagation via the stochastic map built from those universal stochastic maps reproduces up to a prefactor exactly the evolution of the quantum mechanical state with the corresponding quantum algorithm, leading to an automated translation of a quantum algorithm to a stochastic classical algorithm. We implement several well-known quantum algorithms, analyse the scaling of the needed number of realizations with the number of qubits, and highlight the role of destructive interference for the cost of the emulation.

Quantum Mechanical Study of Protonation of Oxygen Ligands in the Laccase Active Site Based on X-Ray Structures of Subatomic Resolution

Laccases are enzymes catalyzing oxidation of a wide range of organic and inorganic substrates accompanied by molecular oxygen reduction to water. Previously studies of oxygen reduction by laccases have recently been reported. They were based on single-crystal serial X-ray crystallography with increasing absorption doses at subatomic resolution, As a result, coordinates of all non-hydrogen atoms of the active site have been determined with high precision for both oxidized and reduced states of the enzyme. Those data can be used to clarify the mechanism of molecular oxygen reduction by laccases. However, the X-ray data lack information about protonation states of the oxygen ligands involved. Applying quantum mechanical calculations, in the present work protonation of oxygen ligands in the active site of laccase was determined for both reduced and oxidized states of the enzyme (the stable states observed in experiments at reduction of molecular oxygen in laccase). The high precision of X-ray-determined atom coordinates allowed us to simplify preliminary calculations of molecular mechanics for models used in the quantum mechanical calculations.

Testing and Optimizing the Drude Polarizable Force Field for Blocked Amino Acids Based on High-Level Quantum-Mechanical Energy Surfaces

The correct reproduction of conformational substates of amino acids was tested for the CHARMM Drude polarizable force field. This was achieved by evaluating the reorganization energies for all low lying energy minima occurring in all 15 neutral blocked amino acids on a quantum-mechanical (QM) energy surface at the MP2/cc-pVDZ level. The results indicate that the bonded parameters of the N-acetyl (ACE) and N-Methylamide (CT3) blocking groups lead to significant discrepancies. A reparametrization of five bond angles significantly improved the agreement with the QM energy surface. The corrected Drude force field exhibits almost the same average reorganization energies relative to the MP2 energy surface as the AM1 and PM3 semi-empirical methods.

The Geometric Algebra Lift of Qubits and Beyond

The Geometric Algebra formalism opens the door to developing a theory upgrading conventional quantum mechanics. Generalizations, stemming from implementation of complex numbers as geometrically feasible objects in three dimensions; unambiguous definition of states, observables, measurements bring into reality clear explanations of conventional weird quantum mechanical features, particularly the results of double split experiments where particles create diffraction patterns inherent to wave diffraction. This weirdness of the double split experiment is milestone of all further difficulties in interpretation of quantum mechanics.

Quantum harmonic free energies for biomolecules and nanomaterials

Obtaining the free energy of large molecules from quantum mechanical energy functions is a longstanding challenge. We describe a method that allows us to estimate, at the quantum mechanical level, the harmonic contributions to the thermodynamics of molecular systems of unprecedented size, with modest cost. Using this approach, we compute the vibrational thermodynamics of a series of diamond nanocrystals, and show that the error per atom decreases with system size in the limit of large systems. We further show that we can obtain the vibrational contributions to the binding free energies of prototypical protein-ligand complexes where the exact computation is too expensive to be practical. Our work raises the possibility of routine quantum mechanical estimates of thermodynamic quantities in complex systems.

Electronic Properties of Aldehyde Complexes Using DFT for Electrooptical Activity

Characterization of materials infer for physical and chemical properties that depend on its molecular structure. Structure of molecule has its dependence on respective electrons of molecule under consideration occupying their positions that correspond to changes in density of electrons. Many theories of its kind were developed to study density of electrons with roots from wavefunction method and electron density method. Wavefunction method has its dependence with linear combination of atomic orbitals, Born approximation, variational principle ,potential energy surfaces for development of Huckel theory, Hartree fock self-consistent theory. Electron density method includes Ab-intio method and density functional theory is possible with Kohenberbg-Kohn existence theorem and Kohn Sham formalism. Density functional studies has diverted attention of researches for properties dependent on structure with use of quantum mechanical descriptors that influence chemical reactivity of molecule forming complexes with properties responsible for electrooptical activity. In the present work complexes with p-anisaldehyde were studied with set of anilines using Gaussian 16 package with B3LYP method. Studies in present work were analyzed from computed infrared spectra responsible for formation of complexes with shifts in wavenumbers; quantum mechanical descriptors for electronic properties. A feature of study is that complexes with p-nitroaniline have greater tendency influence on electronic properties responsible for electrooptical activity due to electrophilic nature.