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May 16-17, 2019 | Prague, Czech Republic

International Conference on

Nanomaterials and Nanotechnology

Advanced Nanoscience and Nanotechnology

Joint Event

Journal of Materials Science and Nanotechnology | Volume 3

Mater Sci Nanotechnol, Volume 3

Computing thermo-elasticity of crystalline systems from quasi-static and quasi-har-

monic approximations

Maurizio Destefanis

University of Turin, Italy

n effective algorithm for the quasi-harmonic calculation

of anisotropic thermo-elasticity of materials is discussed

and implemented into the CRYSTAL program for quantum-

mechanical simulations of extended systems. The directional

elastic response of solid compounds is expressed in terms of

the fourth-order

stiffness tensor

: Its components - namely, the

elastic constants – define the stress-strain linear relationships.

One of the main challenges to state-of-the-art methodologies

is that of reliably and efficiently accounting for thermal effects

on solid compounds. The simplest way to accomplish this is by

means of standard harmonic lattice dynamics; however, when

anharmonic thermal effects are totally neglected, the volume

and elastic response do not exhibit any dependence on the

temperature. An easy way to overcome these limitations is

offered by the so-called

quasi-harmonic approximation

: It

explicitly introduces the volume into the expression of the

phonon frequencies, which are still computed at theharmonic

level but at several volumes. The Helmholtz free energy is

then expressed as function of both volume and temperature

(and not just of temperature as it would be at the harmonic

level), thus allowing the thermal expansion of the system to

be determined. Then, the thermo-elastic constants of the

compound are given by the second-order derivatives of the

Helmholtz free energy with respect to strain – normalized by

the volume at that temperature. A simpler approach is also

presented: inside the

quasi-static approximation

, the thermal

dependence of elastic constants is assumed to be due only

to the thermal expansion of the system – the derivatives are

performed on the static energy, which does not include any

thermal contribution. This algorithmhas then been applied to

the forsterite mineral and the results are discussed: It shows

great accuracy with experimental data (especially with the

trends) and good coherency among different DFT functionals.

Speaker Biography

Maurizio Destefanis obtained his BSc andMSc in Chemistry at University of

Turin, Italy. During the degree program, his interests were focused on the

interface between chemistry and computer science, since he developed

software for chemistry during both his theses projects and research activity

in computational chemistry. He specialized into algorithm development

(mainly through the Fortran programming language – imperative and

static) and application design (mainly through the Ruby programming

language – object-oriented and dynamic). Currently, he is working in the

Information Technology field for the company Accenture as a backend Java

developer. In 2011, he was also awarded by the Italian Chemical Society

with the bronze medal at the Italian Chemistry Olympiads competition.

maurizio.destefanis@gmail.com