CMSP Seminar @ICTP Stasi Room: Mal-Soon LEE Tuesday 2 May at 11:00

[Condensed Matter Section]

ICTP Condensed Matter and Statistical Physics Seminar
---------------------------------------------------------------------------

Tuesday, 2 May at 14:00 hrs.

Luigi Stasi Seminar Room, first floor, ICTP Leonardo building
*********************************************************************

Speaker:
Mal-Soon LEE
(Basic & Applied Molecular Foundations, PNNL, Richland, WA, USA)

Title:
Anharmonic Effects on Material Properties at High Temperatures from
Ab Initio Molecular Dynamics Simulations

Abstract:
/Ab initio/molecular dynamics simulation technique is a promising tool 
to study various properties of vibrational spectra, entropy, free 
energy, etc. even at high temperatures. With the harmonic phonon model, 
all interatomic forces are treated as purely harmonic so that the 
equilibrium distance between atoms is independent of temperature. At the 
low temperature regime, this model, commonly used in most quantum 
chemistry codes, can approximately model vibrational properties and free 
energetics. At higher temperatures, however, the harmonic model can 
break down since it cannot explain thermal expansion, where the role of 
anharmonicity becomes very important in the description and 
interpretation of the system. To better describe properties of systems 
at high temperatures, the quasi-harmonic approximation can be. In this 
talk, I will present a few examples to show how the quasi-harmonic 
approximation is used to rigorously evaluate the vibrational density of 
states at elevated temperatures. From this, the quantitative evaluation 
of thermodynamic properties such as entropy, enthalpy, free energy, and 
equilibrium constants can then be inferred. A variety of systems ranging 
from ethanol-adsorption in zeolites (catalysis),[1] water/scCO_2 
/mineral interfaces (carbon sequestration),[2] and Tc-incorporation in 
magnetite (nuclear remediation)[3] are used to illustrate the power of 
this approach.

[1]Alexopoulos, K.; Lee, M.-S.; Liu, Y.; Zhi, Y.; Liu, Y.; Reyniers, 
M.-F.; Marin, G. B.; Glezakou, V.-A.; Rousseau, R.; Lercher, J. A/. J. 
Phys. Chem. C/ *120*, 7172 (2016).

[2]Lee, M.-S.; McGrail, B. P.; Rousseau, R.; Glezakou, V.-G. /Sci. Rep/. 
*5*, 14857 (2015).

[3]Lee, M.-S.; Um, W.; Wang, G.; Krug. A. A.; Lukens, W. W.; Rousseau, 
R.; Glazakou, V.-A. Nat. Commun. *7*, 12067 (2016).