Negative heat capacity of sodium clusters

Reyes-Nava, Juan A.; Garzón, Ignacio L.; Michaelian, K.

doi:10.1103/physrevb.67.165401

Cited by 74 publications

(55 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There are now many persuasive results from simulations and analytic theory to give credence to the negative heat capacities of clusters of adequate size. 6,9,13,[19][20][21][22][23][24][25] Clusters as small as Ar 13 , however, do not exhibit negative heat capacities, even though they do show regions of coexisting phases. On the other hand, Ar 55 does show an S-bend in its microcanonical caloric curve, when the kinetic definition of temperature is used.…”

Section: Heat Capacities Normal and Otherwisementioning

confidence: 99%

Remarks on Negative Heat Capacities of Clusters

Berry¹

2004

Israel Journal of Chemistry

View full text Add to dashboard Cite

show abstract

Section: Heat Capacities Normal and Otherwisementioning

confidence: 99%

Remarks on Negative Heat Capacities of Clusters

Berry¹

2004

Israel Journal of Chemistry

View full text Add to dashboard Cite

show abstract

“…The observed pattern of maxima and minima in the T m N curve cannot be fully explained either by electronic or geometric (icosahedral) shell closings. Despite much theoretical effort [3][4][5][6][7][8][9], no definite explanation for the calorimetry experiments has emerged yet. In this Letter, we show that molecular dynamics (MD) simulations, with an accurate (first-principles) representation of interatomic forces, reproduce and provide an explanation for the calorimetry results.…”

mentioning

confidence: 99%

Anomalous Size Dependence in the Melting Temperatures of Free Sodium Clusters: An Explanation for the Calorimetry Experiments

Aguado

López

2005

Phys. Rev. Lett.

View full text Add to dashboard Cite

The meltinglike transition in unsupported Na N clusters (N 55, 92, 147, 181, 189, 215, 249, 271, 281 and 299) is studied by first-principles isokinetic molecular dynamics simulations. The irregular size dependence of the melting temperatures T m observed in the calorimetry experiments of Schmidt et al.[Nature (London) 393, 238 (1998)] is quantitatively reproduced. We demonstrate that structural effects alone can explain all broad features of experimental observations. Specifically, maxima in T m N correlate with high surface stability and with structural features such as a high compactness degree. DOI: 10.1103/PhysRevLett.94.233401 PACS numbers: 36.40.Ei, 31.15.Qg, 36.40.Sx, 64.70.Dv There is a fundamental interest in understanding the analog of the melting phase transition in small atomic clusters. Classical arguments predict that melting temperatures T m of small particles should show a monotonic decrease from the bulk limit as their sizes shrink. However, Jarrold and co-workers [1] have demonstrated that small gallium and tin clusters melt at temperatures higher than T bulk m . Also, calorimetry experiments by Haberland and co-workers [2] show that the size dependence of T m is not monotonic for Na N clusters in the size range N 50-350. The observed pattern of maxima and minima in the T m N curve cannot be fully explained either by electronic or geometric (icosahedral) shell closings. Despite much theoretical effort [3][4][5][6][7][8][9], no definite explanation for the calorimetry experiments has emerged yet. In this Letter, we show that molecular dynamics (MD) simulations, with an accurate (first-principles) representation of interatomic forces, reproduce and provide an explanation for the calorimetry results.We employ an orbital-free (OF) version of density-functional-theory (DFT) [10], which expresses the energy as an explicit functional of the valence electron density, and pseudopotentials to represent the ionic field acting on the valence electrons. The technical details of our OF-DFT implementation are explained in previous work [5,11]. Here we describe just the main improvements incorporated into our energy functional. Compared to Kohn-Sham (KS) [12] calculations, two new ingredients appear in OF-DFT: (i) an explicit expression for the functional dependence of the noninteracting electron kinetic energy on density, T s n , and (2) if pseudopotentials are employed, they must be local, that is, dependent only on spatial position and not on orbital angular momenta which are simply not defined in OF-DFT. In previous works [5], we employed the second-order gradient expansion for T s n [13] and the local pseudopotential of Fiolhais et al. [14]. Those pseudopotentials were adjusted to reproduce bulk properties within linear-response-theory and might not be optimal for cluster DFT studies. In this work, the T s n functional is given by [11] T s n T vW n T n ; (1)where T vW 1 8 R dr jrnj 2 n is the von Weizsäcker functional, kr 3 2 1=3 nr , k 0 f is the Fermi wave vector corresponding to a mean electron ...

show abstract

“…Here, V ρ(r,T ,N )φ(r)dV = φ T ,N is the average energy which plays the role of an order parameter or reaction coordinate similar to the corresponding one introduced previously [3,10]. Hence, the stability condition now reads…”

Section: A Thermodynamic Stabilitymentioning

confidence: 99%

“…This energetic restriction has been observed, for instance, in the formation of magnetic domains in ferromagnetic materials [6] or in the hysteresis cycles of Li-ion batteries and other energy storage systems [7][8][9]. Even more exotic systems such as atomic nanoclusters with magical numbers show peculiar * isholek.fc@gmail.com † agustiperezmadrid@ub.edu effects on their behavior and properties similar to those of the small systems we will consider here [10,11].…”

Section: Introductionmentioning

confidence: 99%

Thermostatistical description of small systems in nonequilibrium conditions: Energy conversion and harvesting

Santamaría‐Holek

Pérez‐Madrid

2014

Phys. Rev. E

View full text Add to dashboard Cite

Hysteresis cycles are very important features of energy conversion and harvesting devices, such as batteries. The efficiency of these may be strongly affected by the physical size of the system. Here, we show that in systems which are small enough, the existence of physical boundaries which produce nonhomogeneities of the interaction potential gives rise to inflections and barriers in the associated free energy. This in turn brings on irreversible processes which can be triggered under suitable external conditions imposed by a heat bath. As an example, by controlling the temperature, the state of a small system may be impelled to oscillate between two different structural configurations or aggregation states avoiding equilibrium coexistence and therefore dissipating energy. This cyclical behavior associated with a hysteresis cycle may be prototypical of energy conversion, storage, or generating nanodevices, as exemplified by Li-ion insertion batteries.

show abstract

Negative heat capacity of sodium clusters

Cited by 74 publications

References 26 publications

Remarks on Negative Heat Capacities of Clusters

Remarks on Negative Heat Capacities of Clusters

Anomalous Size Dependence in the Melting Temperatures of Free Sodium Clusters: An Explanation for the Calorimetry Experiments

Thermostatistical description of small systems in nonequilibrium conditions: Energy conversion and harvesting

Contact Info

Product

Resources

About