"Thermal Properties of Guest-Free Si136 and Ge136 Clathrates: A First-Principles Study"

Koushik Biswas; Charles Myles; Mahdi Sanati; George S Nolas

doi:10.1063/1.2960580

"Thermal Properties of Guest-Free Si136 and Ge136 Clathrates: A First-Principles Study"

Koushik Biswas, Charles Myles, Mahdi Sanati, George S Nolas

Physics

Research output: Contribution to journal › Article › peer-review

Abstract

We have used the generalized gradient approximation GGA to density functional theory to study the vibrational and thermal properties of guest-free Si136 and Ge136 clathrates. In order to study the effects of supercell size on our results, we have performed both 34 and 136 atom supercell calculations for each material. We find that the 34 atom supercell calculations predict a small frequency downshift in comparison with the 136 atom supercell calculations in the vibrational density of states of both materials. The GGA-predicted phonon frequency of Si136 480 cm−1 at T=0 K obtained from the 136 atom calculations is in very good agreement with the experimental value for Na1Si136 484 cm−1 at T=300 K. Using the results from our 136 atom calculations, we have also calculated the temperature dependence of the vibrational contributions to the Helmholtz free energy, the entropy, and the specific heat CV of the guest-free Si136 and Ge136 clathrates. The predicted and experimental heat capacitie

Original language	English
Pages (from-to)	033535-1 to 033535-5
Journal	Journal of Applied Physics
DOIs	https://doi.org/10.1063/1.2960580
State	Published - Aug 12 2008

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title = "{"}Thermal Properties of Guest-Free Si136 and Ge136 Clathrates: A First-Principles Study{"}",

abstract = "We have used the generalized gradient approximation GGA to density functional theory to study the vibrational and thermal properties of guest-free Si136 and Ge136 clathrates. In order to study the effects of supercell size on our results, we have performed both 34 and 136 atom supercell calculations for each material. We find that the 34 atom supercell calculations predict a small frequency downshift in comparison with the 136 atom supercell calculations in the vibrational density of states of both materials. The GGA-predicted phonon frequency of Si136 480 cm−1 at T=0 K obtained from the 136 atom calculations is in very good agreement with the experimental value for Na1Si136 484 cm−1 at T=300 K. Using the results from our 136 atom calculations, we have also calculated the temperature dependence of the vibrational contributions to the Helmholtz free energy, the entropy, and the specific heat CV of the guest-free Si136 and Ge136 clathrates. The predicted and experimental heat capacitie",

author = "Koushik Biswas and Charles Myles and Mahdi Sanati and Nolas, {George S}",

year = "2008",

month = aug,

day = "12",

doi = "10.1063/1.2960580",

language = "English",

pages = "033535--1 to 033535--5",

journal = "Journal of Applied Physics",

publisher = "American Institute of Physics",

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TY - JOUR

T1 - "Thermal Properties of Guest-Free Si136 and Ge136 Clathrates: A First-Principles Study"

AU - Biswas, Koushik

AU - Myles, Charles

AU - Sanati, Mahdi

AU - Nolas, George S

PY - 2008/8/12

Y1 - 2008/8/12

N2 - We have used the generalized gradient approximation GGA to density functional theory to study the vibrational and thermal properties of guest-free Si136 and Ge136 clathrates. In order to study the effects of supercell size on our results, we have performed both 34 and 136 atom supercell calculations for each material. We find that the 34 atom supercell calculations predict a small frequency downshift in comparison with the 136 atom supercell calculations in the vibrational density of states of both materials. The GGA-predicted phonon frequency of Si136 480 cm−1 at T=0 K obtained from the 136 atom calculations is in very good agreement with the experimental value for Na1Si136 484 cm−1 at T=300 K. Using the results from our 136 atom calculations, we have also calculated the temperature dependence of the vibrational contributions to the Helmholtz free energy, the entropy, and the specific heat CV of the guest-free Si136 and Ge136 clathrates. The predicted and experimental heat capacitie

AB - We have used the generalized gradient approximation GGA to density functional theory to study the vibrational and thermal properties of guest-free Si136 and Ge136 clathrates. In order to study the effects of supercell size on our results, we have performed both 34 and 136 atom supercell calculations for each material. We find that the 34 atom supercell calculations predict a small frequency downshift in comparison with the 136 atom supercell calculations in the vibrational density of states of both materials. The GGA-predicted phonon frequency of Si136 480 cm−1 at T=0 K obtained from the 136 atom calculations is in very good agreement with the experimental value for Na1Si136 484 cm−1 at T=300 K. Using the results from our 136 atom calculations, we have also calculated the temperature dependence of the vibrational contributions to the Helmholtz free energy, the entropy, and the specific heat CV of the guest-free Si136 and Ge136 clathrates. The predicted and experimental heat capacitie

U2 - 10.1063/1.2960580

DO - 10.1063/1.2960580

M3 - Article

SP - 033535-1 to 033535-5

JO - Journal of Applied Physics

JF - Journal of Applied Physics

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