10 m

Modelling superheating of small Ga and Al clusters

Krista G. SteenbergenNicola Gaston, Dmitri Schebarchov, Shaun C. Hendy

Overview

• Background• First-principles

molecular dynamics• Multiple histogram

specific heat curves• Structural analysis

Dr. Gaston

Drs. Schebarchov and Hendy

Melting of Small Particles

A. A. Shvartsburg, M. F. Jarrold. PRL 85, 2530 (2000)

Ph. Buffat, J.-P. Borel, PRA 13, 2287 (1976)

Tm 1/RTm 1/R

Small Al and Ga clusters

G.A. Breaux et al, J. Am. Chem. Soc. 126, 8628-9 (2004)

C. M. Neal, A. K. Starce, M. F. Jarrold, PRB 76, 054113 (2007)

Bulk gallium

Bulk gallium

E. Voloshina, K. Rosciszewski and B. Paulus, Phys. Rev. B 79, 045113 (2009)

S.C. Hendy and N. Gaston, Superheating in Nanoparticles, The Handbook of Nanophysics (2010)

Gallium Clusters

Underlying mechanism for cluster superheating?Role of structure?Dimeric nature?

Microcanonical Molecular Dynamics

Constant NVE

Positions of atoms/electr

ons

Calculate forces

E1 10,000 MD stepsE2 10,000 MD stepsE3 10,000 MD steps…

E19 10,000 MD steps

First-principles molecular dynamics

VASP software package Born-Oppenheimer MD

Schrödinger Newton

electrons ions

Monte Carlo “Dice Roll”

Computational Resources

• BlueGene/L– University of Canterbury

– 2048 processors

• Carbon Cluster– Argonnne National Laboratory

– 2784 processors

• Kakapo Cluster– Industrial Research Ltd.

– 128 processors

• BlueGene/P– UofC

– 8192 processors (!!)

Multiple Histogram Specific Heats

Cluster Melting Curve – Ga20

Ga20

Ga20+

S. Krishnamurty et al.. PRB 73, 045406 (2006)

Cluster Melting Curves – Ga20+

Ga20+, less accurate potential than Ga20

Ga20+

S. Krishnamurty et al.. PRB 73, 045406 (2006)

Cluster Melting Curves – Al20

C. M. Neal et al.. PRB 76, 054113 (2007)

0 K 600 K 1200 K

Al20Al20

+

Cluster Melting Curves

Cluster Melting Curve – Ga33

Ga33

Ga33+

G.A. Breaux et al, J. Am. Chem. Soc. 126, 8628-9 (2004)

Structural Analysis

• Time, temp or energy, N x atoms, structure measure

250 K 800 K 1150 K

Structural Analysis

Ga20, 600 K Ga20, 1150 K

Future Work

• Continue MD on more cluster sizes– Gan and Aln for n=20-34

• Structural analysis– Common Neighbor Analysis– Lindemann Index

Many Thanks

• Dr. Nicola Gaston and Dr. Shaun C. Hendy

• Dmitri Schebarchov and Amanda Parker

• The Marsden Fund

• MacDiarmid Institute for Advanced Materials and Nanotechnology

• Industrial Research, Ltd.

• BlueFern

• Argonne National Laboratory