اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGlobal Potential Energy Minima of $(H_2O)_n$ Clusters on Graphite: A Comparative Study of the TIP$N$P ($N=3,4,5$) Family
145
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The water-graphite interaction potential proposed recently (Gonzalez et al.emph{J. Phys. Chem. C} textbf{2007}, emph{111}, 14862), the three TIP$N$P ($N=3,:4,:5$) water-water interaction models, and basin-hopping global optimization are used to find the likely candidates for the global potential energy minima of (H$_{2}$O)$_{n}$ clusters with $nleq21$ on the (0001)-surface of graphite and to perform a comparative study of these minima. We show that, except for the smaller clusters ($n<6$), for which ab-initio results are available, the three water-water potential models provide mostly inequivalent conformations. While TIP3P seems to favor monolayer water structures for $n<18$, TIP4P and TIP5P favor bilayer or volume structures for $n>6$. These $n$ values determine the threshold of dominance of the hydrophobic nature of the water-graphite interaction at the nanoscopic scale for these potential models.
قيم البحث
اقرأ أيضاً
We present structure calculations of neutral and singly ionized Mg clusters of up to 30 atoms, as well as Na clusters of up to 10 atoms. The calculations have been performed using density functional theory (DFT) within the local (spin-)density approx
imation, ion cores are described by pseudopotentials. We have utilized a new algorithm for solving the Kohn-Sham equations that is formulated entirely in coordinate space and, thus, permits straightforward control of the spatial resolution. Our numerical method is particularly suitable for modern parallel computer architectures; we have thus been able to combine an unrestricted simulated annealing procedure with electronic structure calculations of high spatial resolution, corresponding to a plane-wave cutoff of 954eV for Mg. We report the geometric structures of the resulting ground-state configurations and a few low-lying isomers. The energetics and HOMO-LUMO gaps of the ground-state configurations are carefully examined and related to their stability properties. No evidence for a non-metal to metal transition in neutral and positively charged Mg clusters is found in the regime of ion numbers examined here.
We present a new theoretical framework for modelling the fusion process of Lennard-Jones (LJ) clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster
growing paths up to the cluster sizes of up to 150 atoms. We demonstrate that in this way all known global minima structures of the LJ-clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence for the clusters of noble gas atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence on cluster size of the second derivative of the binding energy per atom calculated for the chain of LJ-clusters based on the icosahedral symmetry with the peaks in the abundance mass spectra experimentally measured for the clusters of noble gas atoms. Our method serves an efficient alternative to the global optimization techniques based on the Monte-Carlo simulations and it can be applied for the solution of a broad variety of problems in which atomic cluster structure is important.
Most theoretical investigations about titanium oxide clusters focus on (TiO$_2$)$_n$. However, many Ti$_n$O$_m$ clusters with $m eq 2n$ are produced experimentally. In this work, first-principles calculations are performed to probe the evolution of T
i$_n$O$_m$ clusters. Our investigations show that for $n=3$-$11$, there exist one relatively stable specie; while for $n=12$-$18$, there are two relatively stable species: Ti-rich and O-rich species. HOMO-LOMO calculations show that the gap can be tuned by changing the size and configurations of Ti$_n$O$_m$ clusters. Our investigation provides insights into the evolution of cluster-to-bulk process in titanium oxide.
We have measured the spontaneous neutral particle emission from copper cluster anions (Cu$_n^-$, $n=3-6$) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the DESIREE (Double ElectroStatic Ion Ring ExpEriment) facilit
y at Stockholm University. The measured rate of emission from the stored Cu$_3^-$ ions follows a single power law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu$_3$ as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu$_4^-$, Cu$_5^-$ and Cu$_6^-$ are well-described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu$_6^-$ ions that were excited by 1.13 eV or 1.45 eV photons after 46 milliseconds of storage.
Feynman-Hibbs (FH) effective potentials constitute an appealing approach for investigations of many-body systems at thermal equilibrium since they allow us to easily include quantum corrections within standard classical simulations. In this work we a
pply the FH formulation to the study of Ne$_N$-coronene clusters ($N=$ 1-4, 14) in the 2-14 K temperature range. Quadratic (FH2) and quartic (FH4) contributions to the effective potentials are built upon Ne-Ne and Ne-coronene analytical potentials. In particular, a new corrected expression for the FH4 effective potential is reported. FH2 and FH4 cluster energies and structures -obtained from energy optimization through a basin-hoping algorithm as well as classical Monte Carlo simulations- are reported and compared with reference path integral Monte Carlo calculations. For temperatures $T> 4$ K, both FH2 and FH4 potentials are able to correct the purely classical calculations in a consistent way. However, the FH approach fails at lower temperatures, especially the quartic correction. It is thus crucial to assess the range of applicability of this formulation and, in particular, to apply the FH4 potentials with great caution. A simple model of $N$ isotropic harmonic oscillators allows us to propose a means of estimating the cut-off temperature for the validity of the method, which is found to increase with the number of atoms adsorbed on the coronene molecule.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
