Search results for "Physics - Chemical Physics"
showing 10 items of 172 documents
Assessment of the Performance of DFT Functionals Using Off-Diagonal Hypervirial Relationships
2021
Off-diagonal hypervirial relationships, combined with quantum mechanical sum rules of charge-current conservation, offer a way for testing electronic excited-state transition energies and moments, which does not need any external reference. A number of fundamental relations were recast into absolute deviations from zero, which have been used to assess the performance of some popular DFT functionals. Extended TD-DFT calculations have been carried out for a pool of molecules chosen to the purpose, adopting a large basis set to ensure high quality results. A general agreement with previous benchmarks is observed.
CPMD simulation of Cu2+ -- phenylalanine complex under micro-solvated environment
2013
The study combines DFT calculations and CPMD simulations to investigate the structures of phenylalanine-copper (II) ([Phe-Cu]2+) complexes and the micro-solvation processes. ....It is found that the phenylalanine moiety appears to be in the neutral form in isolated and mono-hydrated complexes, but in the zwitterionic form in other hydrated complexes (with n no less than 2). .... The present CPMD simulations reveal that the maximum coordination of Cu2+ in the presence of the Phe ligand does not exceed four: the oxygen atoms from three water molecules and one carboxyl oxygen atom of Phe. Any excess water molecules will migrate to the second solvation shell. Moreover a unique structural motif …
Gluconate and hexitols effects on C-S-H solubility
2021
This study investigates the effect of gluconate, a carboxylate ion, and three uncharged hexitols, D-sorbitol, D-mannitol and D-galactitol on the solubility of C-S-H. Thermodynamic modeling was used to determine the kind and amount of Ca-organic-silicate-OH complexes that potentially form in the conditions studied. All the organics form complexes with calcium and hydroxide, In addition, heteropolynuclear organics complexes with calcium, hydroxide and silicate are observed at high pH values and high calcium concentrations with the exception of mannitol. The strength of complexation with silicate decreases from gluconate > sorbitol > galactitol. The adsorption of the selected organics on…
On the calculation of potential of mean force between atomistic nanoparticles
2018
We study the potential of mean force (PMF) between atomistic silica and gold nanoparticles in the vacuum by using molecular dynamics simulations. Such an investigation is devised in order to fully characterize the effective interactions between atomistic nanoparticles, a crucial step to describe the PMF in high-density coarse-grained polymer nanocomposites. In our study, we first investigate the behavior of silica nanoparticles, considering cases corresponding to different particle sizes and assessing results against an analytic theory developed by Hamaker for a system of Lennard-Jones interacting particles [H. C. Hamaker, Physica A, 1937, 4, 1058]. Once validated the procedure, we calculat…
Zero-Field J-spectroscopy of Quadrupolar Nuclei
2020
Zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is a version of NMR that allows studying molecules and their transformations in the regime dominated by intrinsic spin-spin interactions. While spin dynamics at zero magnetic field can be probed indirectly, J-spectra can also be measured at zero field by using non-inductive sensors, for example, optically-pumped magnetometers (OPMs). A J-spectrum can be detected when a molecule contains at least two different types of magnetic nuclei (i.e., nuclei with different gyromagnetic ratios) that are coupled via J-coupling. Up to date, no pure J-spectra of molecules featuring the coupling to quadrupolar nuclei were reported. Here we sho…
The Heats of Reactions. Calorimetry and Van't-Hoff. 3
2001
Earlier, the author found that for the biggest part of chemical reactions the law of conservation of energy must have the following form: dU=dQ+PdV+SUM. In the present paper this result is confirmed by other experiments.
Battery Diagnostics with Sensitive Magnetometry
2019
The ever-increasing demand for high-capacity rechargeable batteries highlights the need for sensitive and accurate diagnostic technology for determining the state of a cell, for identifying and localizing defects, or for sensing capacity loss mechanisms. Here, we demonstrate the use of atomic magnetometry to map the weak induced magnetic fields around a Li-ion battery cell as a function of state of charge and upon introducing mechanical defects. These measurements provide maps of the magnetic susceptibility of the cell, which follow trends characteristic for the battery materials under study upon discharge. In addition, the measurements reveal hitherto unknown long time-scale transient inte…
Coupled-cluster theory for atoms and molecules in strong magnetic fields
2015
An implementation of coupled-cluster (CC) theory to treat atoms and molecules in finite magnetic fields is presented. The main challenges for the implementation stem from the magnetic-field dependence in the Hamiltonian, or, more precisely, the appearance of the angular momentum operator, due to which the wave function becomes complex and which introduces a gauge-origin dependence. For this reason, an implementation of a complex CC code is required together with the use of gauge-including atomic orbitals to ensure gauge-origin independence. Results of coupled-cluster singles-doubles-perturbative-triples (CCSD(T)) calculations are presented for atoms and molecules with a focus on the depende…
Virtual Orbital Many-Body Expansions: A Possible Route towards the Full Configuration Interaction Limit
2017
In the present letter, it is demonstrated how full configuration interaction (FCI) results in extended basis sets may be obtained to within sub-kJ/mol accuracy by decomposing the energy in terms of many-body expansions in the virtual orbitals of the molecular system at hand. This extension of the FCI application range lends itself to two unique features of the current approach, namely that the total energy calculation can be performed entirely within considerably reduced orbital subspaces and may be so by means of embarrassingly parallel programming. Facilitated by a rigorous and methodical screening protocol and further aided by expansion points different from the Hartree-Fock solution, al…
Convergence of coupled cluster perturbation theory.
2016
The convergence of a recently proposed coupled cluster (CC) family of perturbation series [Eriksen, J. J. et al., J. Chem. Phys. 140, 064108 (2014)], in which the energetic difference between two CC models - a low-level parent and a high-level target model - is expanded in orders of the M{\o}ller-Plesset (MP) fluctuation potential, is investigated for four prototypical closed-shell systems (Ne, singlet methylene, distorted HF, and the fluoride anion) in standard and augmented basis sets. In these investigations, energy corrections of the various series have been calculated to high orders and their convergence radii determined by probing for possible front- and back-door intruder states, the…