Free Ab-initio Molecular Dynamics Research Articles

An Orbital Free Ab-initio Molecular Dynamics Study of Liquid Pt for Static and Dynamic Properties

Using the orbital free ab-initio molecular dynamics (OF-AIMD) simulation scheme we have examined the static and dynamic properties of liquid Pt at the thermodynamic state near to its melting point. In this simulation scheme, the Hohenberg and Kohn orbital free density functional theory (OF-DFT) has been employed. In OF-DFT, we have estimated the electron-ion interaction by a local pseudopotential and also controlled the exchange-correlation energy functional by using the local density approximation (LDA). The static properties, for instance, static structure factor, S(q), pair correlation function, g(r), coordination number, Nc, and isothermal compressibility, κT, are examined. Using the familiar single-particle dynamics, the self-diffusion coefficient and self-intermediate scattering function are studied. It is found that the self-intermediate scattering function is controlled by the selfdiffusion coefficient. While for studying the collective dynamics of the system, we have calculated velocity of sound from the longitudinal dispersion relation and shear viscosity from the transverse current correlation function, JT(q, t). The OF-AIMD results are nicely fit with the theoretical and experimental results accessible to us for comparison. Dhaka Univ. J. Sci. 69(3): 179-185, 2022 (June)

Static and Dynamic Properties of Elemental Liquid Pd: An Orbital Free Molecular Dynamic Study

We have studied the static and dynamic properties of liquid metal, namely Pd at thermodynamic state T=1853K within the scope of the orbital free ab-initio molecular dynamics (OF-AIMD) simulation technique. In this simulation process, electronic energy is calculated by using the Hohenberg-Kohn version of DFT. Here the electron-ion interaction energy functional is approximated by a local pseudopotential prescribed by Bhuiyan et al. The local density approximation is used to describe the exchange-correlation energy functional. The static structure factor, S(q), pair distribution function, g(r), coordination number, Nc, and isothermal compressibility, κT, are studied which are familiar as static properties. The single particle and collective dynamics namely diffusion coefficient, dynamic structure factor, velocity of sound, shear viscosity etc. are also studied. The results of calculation agree well with experimental as well as other theoretical values.

Static and dynamic properties of liquid Fe: An OF-AIMD simulation study

A study of static and dynamic properties for liquid Fe using orbital free ab-initio molecular dynamics (OF-AIMD) simulation technique at thermodynamic states near the melting point is presented for the first time. The OF-AIMD simulation method is related to the density functional theory. Different static magnitudes such as static structure factors, isothermal compressibility, pair distribution functions and coordination numbers obtained from simulation are described. And the dynamic properties for both single and collective dynamics such as dynamic structure factors, diffusion coefficients, adiabatic sound velocity, and shear viscosity are also reported. The evaluated results for static and dynamic properties are found to be good in agreement with the available experimental data. Most importantly, a comparison with some KS-AIMD results shows that the degree of accuracy of the present OF-AIMD study is as good as that of the KS-AIMD.

Orbital free ab initio study of static and dynamic properties of some liquid transition metals

Several static and dynamic properties of liquid transition metals Cr, Mn and Co are studied for the first time using the orbital free ab-initio molecular dynamics simulation (OF-AIMD). This method is based on the density functional theory (DFT) which accounts for the electronic energy of the system whereas the interionic forces are derived from the electronic energy via the Hellman-Feynman theorem. The external energy functional is treated with a local pseudopotential. Results are reported for static structure factors, isothermal compressibility, diffusion coeffcients, sound velocity and viscosity and comparison is performed with the available experimental data and other theoretical calculations.

Structure and dynamics of high-pressure Na close to the melting line: Anab initiomolecular dynamics study

The melting curve of sodium for a pressure range up to 100 GPa has been evaluated by the orbital free ab initio molecular dynamics method. This method uses the electronic density as the basic variable combined with an approximate electronic kinetic energy functional and a local ionic pseudopotential and makes it possible to perform simulations with a large number of particles and for long simulation times. The calculated melting curve shows a maximum melting temperature at a pressure around 30 GPa followed by a steep decrease up to 100 GPa. For various pressures and temperatures we have evaluated several static properties, including average and local structure, electronic properties, like the electron localization function (ELF), and dynamic properties, both single-particle and collective ones, from which some transport coefficients are deduced. Despite the accurate reproduction of the available experimental data, we do not observe any indication of an early transition from a bcc-like to an fcc-like liquid, as suggested previously by other authors, but rather pressure-induced change in the variation of icosahedral-like order and bcc-like order, with no sign of fcc-like structures in the whole liquid range studied. We also consider the evolution of the ELF within this type of local arrangement upon pressurization. In the dynamic realm, we find an enlarged wave-vector region where atomic collisions play an important role in the dynamic properties of the system as pressure is increased and temperature decreased along the melting line, leading to a peculiar behavior of the dynamic properties.

Static and dynamic properties of liquid Zn, Cd and Hg divalent metals: An orbital free ab initio molecular dynamics study

We report a study on several static and dynamic properties of liquid Zn, Cd, and Hg divalent metals at thermodynamic conditions near their respective triple points. The calculations have been carried out by using the orbital free ab initio molecular dynamics (OF-AIMD) simulation technique which is based on the density functional theory. Results are reported for a range of static structural magnitudes, such as static structure factors, pair distribution functions and coordination numbers. A comparison with the available X-ray diffraction data shows that the OF-AIMD method can provide a reasonable description of the static structure. As for the dynamic properties, results are reported for both single and collective dynamics. The calculated dynamic structure factors show side peaks which point to the existence of collective density excitations. Finally, we report the calculation of some transport coefficients which are compared with the corresponding experimental data. Comparison with other AIMD methods show some discrepancies in dynamic properties, and possible modifications of the approach used in this study are suggested accordingly.

Orbital free ab initio molecular dynamics simulation study of some static and dynamic properties of liquid noble metals

Several static and dynamic properties of liquid Cu, Ag and Au at thermodynamic states near their respective melting points, have been evaluated by means of the orbital free ab-initio molecular dynamics simulation method. The calculated static structure shows good agreement with the available X-ray and neutron diffraction data. As for the dynamic properties, the calculated dynamic structure factors point to the existence of collective density excitations along with a positive dispersion for l-Cu and l-Ag. Several transport coefficients have been obtained which show a reasonable agreement with the available experimental data.

An Orbital-free Molecular Dynamics Study of Static and Dynamic Properties of Liquid Sn

The static and dynamic properties of liquid Sn at two different thermodynamic states have been studied from the Orbital Free Ab-Initio Molecular Dynamics (OFAIMD) simulation method. This method is based on the density functional theory (DFT) of Hohenberg and Kohn. The exchange and correlation interaction is described here with the local density approximation (LDA). We, in this study, have developed a pseudopotential model to describe the external non-Coulombic interaction acting on an electron; this is an essential ingredient of the theory. We have studied several static and dynamic properties of the system. The calculated results are found to be good in agreement with the available experimental data. They are also found to be of similar accuracy as those of other ab-initio studies.

Microscopic dynamics in liquid binary alloys: orbital-free ab-initio molecular dynamics studies

We report an ab-initio molecular dynamics study on the collective excitations in several s-p bonded liquid binary alloys. Results are reported for the Li–Na, Li–Mg, K–Cs and Li–Ba liquid alloys at different concentrations, which display mass ratios ranging from ≈ 3 for Li–Na to ≈ 20 for Li–Ba, and varying ordering tendencies, ranging from strong homocoordinating in Li–Na to mildly heterocoordinating for one concentration of Li–Ba. The study has been carried out using the orbital free ab-initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. We analyze the dependence of the collective modes on the concentration and the mass ratio of the alloy, finding a common behaviour for all systems notwithstanding the different ordering tendencies.

Atomic clustering in liquid Al3Li: An orbital free ab initio study

We report the results of an orbital free ab initio molecular dynamics simulation of the structure and some dynamic properties of liquid Al3Li at T=1000K, using 1000 particles and averaging over a total of 21ps. The structure factors show a clear prepeak at a very small wavenumber, ≈0.5Å−1, suggesting the presence of large clusters in the alloy. The analysis of the distribution of coordination numbers suggests the presence of two types of Li atoms, giving some support to a model of clusters swimming on a ‘normal’ alloy, proposed in the literature for Tl-rich liquid Cs–Tl alloys.

Structural and dynamical properties of liquid Si: An Orbital-free molecular dynamics study

Several static and dynamic properties of liquid silicon near melting have been determined from an orbital free ab initio molecular dynamics simulation. The calculated static structure is in good agreement with the available x ray and neutron diffraction data. The dynamical structure shows collective density excitations with an associated dispersion relation which closely follows recent experimental data. It is found that liquid silicon cannot sustain the propagation of shear waves which can be related to the power spectrum of the velocity autocorrelation function. Accurate estimates have also been obtained for several transport coefficients. The overall picture is that the dynamic properties have many characteristics of the simple liquid metals although some conspicuous differences have been found.

Collective modes in liquid binary alloys. An ab initio molecular dynamics study of theLiMg and LiBa alloys

We report a study on several structural and dynamical properties of the liquid Li–Mg andLi–Ba alloys. The study has been carried out by means of the orbital free ab initiomolecular dynamics method, combined with local ionic pseudopotentials constructedwithin the same framework. The results show good agreement with the availableexperimental data, accounting fairly well for the different ordering tendenciesexhibited by these alloys. We analyse the dependence of the longitudinal andtransverse collective modes on the concentration and the mass ratio of the alloy,with the latter ranging from to .

Density fluctuations in the liquid Na–Cs alloy.: An ab initio molecular dynamics study

We present results for several structural and dynamical properties of liquid Na–Cs alloys. The study has been carried out using orbital free ab initio molecular dynamics, combined with local ionic pseudopotentials constructed within the same framework. The results show good agreement with the available experimental data, reproducing the phase separating tendency exhibited by this alloy.

Dynamical properties of liquid Al near melting: An orbital-free molecular dynamics study

The static and dynamic structure of liquid Al is studied using the orbital free ab-initio molecular dynamics method. Two thermodynamic states along the coexistence line are considered, namely T = 943 K and 1323 K for which X-ray and neutron scattering data are available. A new kinetic energy functional, which fulfills a number of physically relevant conditions is employed, along with a local first principles pseudopotential. In addition to a comparison with experiment, we also compare our ab-initio results with those obtained from conventional molecular dynamics simulations using effective interionic pair potentials derived from second order pseudopotential perturbation theory.

Orbital free ab initio molecular dynamics study of liquid Al near melting

The orbital free ab initio molecular dynamics method is applied to study the static and dynamic structure of liquid Al near the triple point. The method uses a new kinetic energy functional, along with a local pseudopotential constructed within the same kinetic energy functional. The results obtained for the dynamic structure factor are compared with recent experimental data.

Orbital free ab initio molecular dynamics study of expanded liquid Cs

Orbital free ab initio molecular dynamics is applied to study the static structure and some dynamic properties of liquid Cs at several states along the liquid–vapour coexistence line. Two different kinetic energy functionals are used, namely, the Thomas–Fermi–von Weizsäcker functional and a simplified average density one, and the comparison with experimental data favours the latter, especially at high temperatures. We also show that the approximation of the electron density by a superposition of pseudatomic densities is poor at high temperatures, while acceptable near the triple point. However, the pseudoatom density predicted by linear response theory appears to be too diffuse even close to the triple point.