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Full Record Details
Persistent URL
http://purl.org/net/epubs/work/49617
Record Status
Checked
Record Id
49617
Title
Effect of quantization of vibrations on the structural properties of crystals
Contributors
I Scivetti (Queen's U., Belfast)
,
NI Gidopoulos (STFC Rutherford Appleton Lab.)
,
J Kohanoff (Queen's U., Belfast)
Abstract
We study the structural effects produced by the quantization of vibrational degrees of freedom in periodic crystals at zero temperature. To this end we introduce a methodology based on mapping a suitable subspace of the vibrational manifold and solving the Schrödinger equation in it. A number of increasingly accurate approximations ranging from the quasiharmonic approximation (QHA) to the vibrational self-consistent field (VSCF) method and the exact solution are described. A thorough analysis of the approximations is presented for model monatomic and hydrogen-bonded chains, and results are presented for a linear H-F chain where the potential-energy surface is obtained via first-principles electronic structure calculations. We focus on quantum nuclear effects on the lattice constant and show that the VSCF is an excellent approximation, meaning that correlation between modes is not extremely important. The QHA is excellent for covalently bonded mildly anharmonic systems, but it fails for hydrogen-bonded ones. In the latter, the zero-point energy exhibits a nonanalytic behavior at the lattice constant where the H atoms center, which leads to a spurious secondary minimum in the quantum-corrected energy curve. An inexpensive anharmonic approximation of noninteracting modes appears to produce rather good results for hydrogen-bonded chains for small system sizes. However, it converges to the incorrect QHA results for increasing size. Isotope effects are studied for the first-principles H-F chain. We show how the lattice constant and the H-F distance increase with decreasing mass and how the QHA proves to be insufficient to reproduce this behavior.
Organisation
ISIS
,
ISIS-THEORY
,
STFC
Keywords
Physics
Funding Information
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Language
English (EN)
Type
Details
URI(s)
Local file(s)
Year
Journal Article
Phys Rev B
78 (2008): 224108.
doi:10.1103/PhysRevB.78.224108
2008
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