Control of near-degeneracy effects and dynamical correlation in atoms molecules is within sight, thanks to an economical method that mixes configuration interaction (CI) density functional theory (DFT). The influence the size configuration-space has been studied for light systems including elements first second period Periodic Table.

Abstract Using recent calculations we review some well‐known aspects of density functional theory: the Hohenberg–Kohn theorems, Kohn–Sham method, adiabatic connection, and approximations local nature. Emphasis is put upon using model Hamiltonians, which noninteracting or physical ones are just particular cases. The Hamiltonians allow us to produce multireference theory continuously switch system. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 166–190,

In order to assess the ability of theory describe properly dispersive interactions that are ubiquitous in peptide and protein systems, an isolated short chain has been studied using both gas-phase laser spectroscopy quantum chemistry. The experimentally observed coexistence extended form a folded supersonic expansion was found result from comparable Gibbs free energies for two species under high-temperature conditions (≤320 K) resulting desorption technique used vaporize molecules. These...

In this study, we used ReaxFF reactive force field molecular dynamics (MD) simulations to investigate the associated with reactivity at sodium aluminosilicate (NAS) glass–water interface. By combining van Hove correlation functions and visual analysis of individual trajectories, found that when a Na+ ion leaves its initial position glass surface under effect water, it can be replaced either by H+ or another diffused Na+, resulting in (Na+ ⇌ H+) exchange Na+) exchange, respectively. These...

An atomistic understanding of the mechanisms that govern borosilicate glass–water interface is highly needed to obtain initial assessments phenomena occurring during degradation nuclear waste forms. To this end, we have simulated a structural model sodium glass using classical molecular dynamics (CMD) simulations followed by Car–Parrinello ab initio (AIMD) simulation and periodic density functional theory (DFT) calculations study both reactivity water adsorption events on glass. The obtained...

Among the forces responsible for shaping proteins, interactions between side chains of aromatic residues play an important role as they are involved in secondary and tertiary structures proteins contributing to formation hydrophobic domains. The purpose this paper is document interaction two capped dipeptides modeling a segment protein chain having consecutive Phe residues, Ac-Phe-Phe-NH(2) Ac-Phe-D-Phe-NH(2). These molecules have been investigated gas phase by IR/UV double resonance...

We study reactivity and leaching at the calcium sodium borosilicate (CNBS)-water interface by means of a Car-Parrinello ab initio molecular dynamics simulation over time 100 ps. With an emphasis on comparison between behaviors Ca2+ Na+ cations CNBS glass-water interface, different mechanism events during trajectory are revealed, discussed, correlated with other density functional theory calculations. show that ions can be released in solution, while cannot leave surface glass. This release...

The first ab initio molecular dynamics simulation of a Gd(III)-based contrast agent in explicit aqueous solution at ambient conditions as used the actual magnetic resonance imaging human bodies is presented. description structure this chelate complex considerably improved with respect to typical force fields and calculations continuum solvent models if open 4f shell Gd included explicitly. solvation-shell revealed be anionic includes rather short hydrogen bond donated by hydroxypropyl arm.

A general spin-projection framework is laid out which allows one to perform ab initio molecular dynamics simulations of antiferromagnetically coupled spin dimers. The method extends the well-established broken-symmetry formalism and systematically consistently improvable. It for accessing structure within same approximation as employed compute exchange coupling constant J such complexes in their low-spin state a function time. resulting time evolution coupling, J(t), can be analyzed most...

A mixed quantum/classical investigation of the dynamical magnetostructural properties, that is, "magnetodynamics," oxidized Anabaena PCC7119 ferredoxin is carried out at room temperature in two distinct conformational states. This protein hosts a [2Fe-2S] cluster which iron centers are antiferromagnetically coupled to an overall low-spin electronic ground state has genuine multireference character. To study magnetodynamics this prosthetic group, approximate spin projection method formulated...

Abstract The adiabatic connection procedure of density functional theory has been applied to two‐ and four‐electron atomic systems by following a nonlinear path that leads from the noninteracting Kohn–Sham reference system physical one. We have calculated exchange correlation energies as interaction strength is increased, well densities corresponding holes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

IR and UV laser spectroscopy of an Ala-based 4-residue model peptide recorded under gas phase isolated conditions provides evidence for the intrinsic stability compact folded structures resembling extremity a β-hairpin, with C14H-bond bridging two ends chain, enables us to assess capabilities new quantum chemistry techniques account dispersive interactions in medium-size molecule.

The proton-exchange process between water and a carbamate has been studied experimentally theoretically in lanthanide-based paramagnetic chemical exchange saturation transfer agent endowed with potential multimodality detection capabilities (optical imaging, or T1 MRI for the Gd(III) analogue). In addition to an in-depth structural analysis by combined approach (using X-ray crystallography, NMR, molecular dynamics), our ab initio simulation aqueous solution sheds light on reaction mechanism...

The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On basis molecular-level details mechanism derived from these simulations aqueous solution, we unravel underlying difference free energies and mechanisms water exchange diastereoisomers. These findings reveal crucial role played by hydrogen-bonding dynamics thus suggest their appropriate...

The electronic relaxation of gadolinium complexes used as MRI contrast agents was studied theoretically by following the short time evolution zero-field-splitting parameters. statistical analysis ab initio molecular dynamics trajectories provided a clear separation between static and transient contributions to zero-field-splitting. For latter, correlation estimated at approximately 0.1 ps. influence ligand also probed replacing one pendant arm our reference macrocyclic complex bulkier...

The photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization fragmentation processes are found to compete. hydrogen-bonded Cis-Cis form GA transformed mainly the open Trans-Trans conformer CO CH3OH fragments their mixed complexes. Different photo-induced behaviours appear depending on matrix. In small amounts Trans-Gauche conformers detected after deposition grow together...

The 4f electrons of lanthanides, because their strong localization in the region around nucleus, are traditionally included a pseudopotential core. This approximation is scrutinized by optimizing structures and calculating interaction energies Gd(3+)(H(2)O) Gd(3+)(NH(3)) microsolvation complexes within plane wave Perdew-Burke-Ernzerhof calculations using ultrasoft pseudopotentials where either core or valence space. Upon comparison to quantum chemical MP2 CCSD(T) reference it found that...

Hyperfine coupling tensors of the water molecule coordinated to Prohance contrast agent in liquid were calculated within and beyond point dipole approximation along an ab initio molecular dynamics trajectory. We observe non-equivalence at short time scales on structural as well magnetodynamical properties inner sphere protons due hydrogen bonds formation with solvent. In addition, influence ultrafast internal motions anisotropic, dipolar, contribution hyperfine couplings was probed thanks a...

In this work, we present ab initio calculations of the zero-field splitting (ZFS) a gadolinium complex [Gd(iii)(HPDO3A)(H2O)] sampled from an molecular dynamics (AIMD) simulation. We perform both post-Hartree-Fock (complete active space self-consistent field—CASSCF) and density functional theory (DFT) ZFS compare contrast methods with experimental data. Two different approximations (TPSS LC-BLYP) were investigated. The magnitude CASSCF is in good agreement experiment, whereas DFT results...

The ability of Density Functional Theory to predict the electronic and magnetic properties semi-infinite graphene with a single bare edge has been probed. In order improve accuracy spin-unrestricted calculations performed semilocal density functionals, higher-level methods including double hybrid functionals many-body perturbation theory have applied polycyclic aromatic hydrocarbons model systems. We show that antiferromagnetic or ferromagnetic tendencies corresponding ground states strongly...

Study of the degenerate exchange involving two xenon atoms and a cryptophane via ab initio molecular dynamics reveals faster reaction rate than for more simple dissociative mechanism self-organization cage.