Search results for "Ab initio molecular dynamics"
showing 10 items of 20 documents
Photoelectron spectra of aluminum cluster anions: Temperature effects and ab initio simulations
1999
Photoelectron (PES) spectra from aluminum cluster anions (from 12 to 15 atoms) at various temperature regimes, were studied using ab-initio molecular dynamics simulations and experimentally. The calculated PES spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures.
Interpretation of the Cu K-edge EXAFS spectra of Cu3N using ab initio molecular dynamics
2020
Financial support provided by ERDF project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. This work was supported by a grant from the Swiss National Supercomputing Centre (CSCS) under the project ID s681 .
Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: the effect of the supercell size
2020
The authors sincerely thank S. Ali, A. Kalinko, and F. Rocca for providing experimental EXAFS data, as well as M. Isupova, V. Kashcheyevs, and A. I. Popov for stimulating discussions. Financial support provided by project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged by D.B. A.K and J.P. would like to thank the support of the Latvian Council of Science project No. lzp-2018/2–0353.
Melting and multipole deformation of sodium clusters
1999
Melting and multipole deformations of sodium clusters with up to 55 atoms are studied using an ab initio molecular dynamics method. The melting temperature regions for Na20, Na40, and Na 55 + are estimated. The melting temperature region determined here for Na 55 + agrees with the one determined experimentally. The dominating deformation type observed at the liquid phase for Na20 and Na40 is octupole deformation and for Na14 and Na 55 + quadrupole deformation.
The amorphous silica-liquid water interface studied by ab initio molecular dynamics (AIMD): local organization in global disorder
2014
International audience; The structural organization of water at a model of amorphous silica-liquid water interface is investigated by ab initio molecular dynamics (AIMD) simulations at room temperature. The amorphous surface is constructed with isolated, H-bonded vicinal and geminal silanols. In the absence of water, the silanols have orientations that depend on the local surface topology (i.e. presence of concave and convex zones). However, in the presence of liquid water, only the strong inter-silanol H-bonds are maintained, whereas the weaker ones are replaced by H-bonds formed with interfacial water molecules. All silanols are found to act as H- bond donors to water. The vicinal silanol…
Ionization potential of Al6 and Al7 as a function of temperature
1999
The temperature-depence of the ionization potential of Al6 and Al7 clusters is studied by using ab initio molecular dynamics. The threshold regions of theoretical photoionization efficiency curves are obtained from the calculated ionization potential distributions by integration and the determined ionization potentials are compared with the experimental ones. Two important effects, which complicate the determination of ionization potential from photoionization efficiency curves, are observed: the thermal tail effect and the isomerization. Also a link between the adiabatic ionization potential and the threshold of the photoionization efficiency curve is discussed. In the case of Al7, this of…
Second generation Car-Parrinello molecular dynamics
2014
Computer simulation methods, such as Monte Carlo or molecular dynamics, are very powerful theoretical techniques to provide detailed and essentially exact informations on rather complex classical many-body problems. With the advent of ab initio molecular dynamics (AIMD), where finite-temperature dynamical trajectories are generated using interatomic forces which are calculated on the fly using accurate electronic structure calculations, the scope of computational research has been greatly extended. This review is intended to outline the basic principles as well as being a survey of the field. Beginning with the derivation of Born–Oppenheimer molecular dynamics, the Car–Parrinello method and…
Bimodal Acidity at the Amorphous Silica/Water Interface
2015
International audience; Understanding the microscopic origin of the acid base behavior of mineral surfaces in contact with water is still a challenging task, for both the experimental and the theoretical communities. Even for a relatively simple material, such as silica, the origin of the bimodal acidity behavior is still a debated topic. In this contribution we calculate the acidity of single sites on the humid silica surface represented by a model for the hydroxylated amorphous surface. Using a thermodynamic integration approach based on ab initio molecular dynamics, we identify two different acidity values. In particular, some convex geminals and some type of vicinals are very acidic (pK…
Study of High-Temperature Behaviour of ZnO by Ab Initio Molecular Dynamics Simulations and X-ray Absorption Spectroscopy
2021
Wurtzite-type zinc oxide (w-ZnO) is a widely used material with a pronounced structural anisotropy along the c axis, which affects its lattice dynamics and represents a difficulty for its accurate description using classical models of interatomic interactions. In this study, ab initio molecular dynamics (AIMD) was employed to simulate a bulk w-ZnO phase in the NpT ensemble in the high-temperature range from 300 K to 1200 K. The results of the simulations were validated by comparison with the experimental Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra and known diffraction data. AIMD NpT simulations reproduced well the thermal expansion of the lattice, and the pronounced …
Atypical titration curves for GaAl12Keggin-ions explained by a joint experimental and simulation approach
2018
Although they have been widely used as models for oxide surfaces, the deprotonation behaviors of the Keggin-ions (MeAl127+) and typical oxide surfaces are very different. On Keggin-ions, the deprotonation occurs over a very narrow pH range at odds with the broad charging curve of larger oxide surfaces. Depending on the Me concentration, the deprotonation curve levels off sooner (high Me concentration) or later (for low Me concentration). The leveling off shows the onset of aggregation before which the Keggin-ions are present as individual units. We show that the atypical titration data previously observed for some GaAl12 solutions in comparison to the originally reported data can be explain…