### Abstract

Understanding, designing, and processing functional metal sulfides are significant challenges in part because of the high temperatures and pressures and the number of secondary phases encountered in these complex systems. In particular, the underlying thermochemical properties are not well understood that would allow prediction of equilibrium conditions and driving forces. In addition, obtaining accurate values for the energetics of metal sulfide systems is far from complete, suggesting application of density functional theory (DFT) calculations. Here, the results of an examination of 69 phases by DFT using 12 exchange-correlation (X-C) functionals indicate that (i) the key source of error in predicting the Gibbs energy of a phase is the enthalpy calculated at 0 K rather than entropy at finite temperatures from phonon calculations and (ii) an improved prediction of the thermodynamic properties at 0 K relies on the selected nonlocal X-C functional such as the hybrid potential. Regarding metal sulfides, we conclude from the present DFT results that (1) the secondary phase Cu2ZnSn3S8, associated with the desired photovoltaic material Cu2ZnSnS4, is not stable at 0 K, but it becomes slightly stable with increasing temperature (i.e., >800 K), primarily due to the vibrational entropy, which makes it difficult to be detected in a typical thin-film growth process; (2) the hybrid X-C functional improves the predicted energetics for most of the layered transition-metal disulfides such as TiS2, MoS2, and WS2, but not for the nonlayered RuS2, OsS2, and IrS2 as well as the layered PdS2; and (3) the formation of the solid-state electrolyte Na3PS4 is thermodynamically favored. We further conclude that accurate energetics as a function of temperature for the materials of interest is feasible to be achieved beyond the semilocal DFT calculations with the key being enthalpy predicted at 0 K.

Original language | English (US) |
---|---|

Article number | 015401 |

Journal | Physical Review Materials |

Volume | 3 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2 2019 |

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### All Science Journal Classification (ASJC) codes

- Materials Science(all)
- Physics and Astronomy (miscellaneous)

### Cite this

*Physical Review Materials*,

*3*(1), [015401]. https://doi.org/10.1103/PhysRevMaterials.3.015401

}

*Physical Review Materials*, vol. 3, no. 1, 015401. https://doi.org/10.1103/PhysRevMaterials.3.015401

**Achieving accurate energetics beyond (semi-)local density functional theory : Illustrated with transition metal disulfides, Cu2ZnSnS4, and Na3PS4 related semiconductors.** / Shang, Shunli; Wang, Yi; Anderson, Timothy J.; Liu, Zi-kui.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Achieving accurate energetics beyond (semi-)local density functional theory

T2 - Illustrated with transition metal disulfides, Cu2ZnSnS4, and Na3PS4 related semiconductors

AU - Shang, Shunli

AU - Wang, Yi

AU - Anderson, Timothy J.

AU - Liu, Zi-kui

PY - 2019/1/2

Y1 - 2019/1/2

N2 - Understanding, designing, and processing functional metal sulfides are significant challenges in part because of the high temperatures and pressures and the number of secondary phases encountered in these complex systems. In particular, the underlying thermochemical properties are not well understood that would allow prediction of equilibrium conditions and driving forces. In addition, obtaining accurate values for the energetics of metal sulfide systems is far from complete, suggesting application of density functional theory (DFT) calculations. Here, the results of an examination of 69 phases by DFT using 12 exchange-correlation (X-C) functionals indicate that (i) the key source of error in predicting the Gibbs energy of a phase is the enthalpy calculated at 0 K rather than entropy at finite temperatures from phonon calculations and (ii) an improved prediction of the thermodynamic properties at 0 K relies on the selected nonlocal X-C functional such as the hybrid potential. Regarding metal sulfides, we conclude from the present DFT results that (1) the secondary phase Cu2ZnSn3S8, associated with the desired photovoltaic material Cu2ZnSnS4, is not stable at 0 K, but it becomes slightly stable with increasing temperature (i.e., >800 K), primarily due to the vibrational entropy, which makes it difficult to be detected in a typical thin-film growth process; (2) the hybrid X-C functional improves the predicted energetics for most of the layered transition-metal disulfides such as TiS2, MoS2, and WS2, but not for the nonlayered RuS2, OsS2, and IrS2 as well as the layered PdS2; and (3) the formation of the solid-state electrolyte Na3PS4 is thermodynamically favored. We further conclude that accurate energetics as a function of temperature for the materials of interest is feasible to be achieved beyond the semilocal DFT calculations with the key being enthalpy predicted at 0 K.

AB - Understanding, designing, and processing functional metal sulfides are significant challenges in part because of the high temperatures and pressures and the number of secondary phases encountered in these complex systems. In particular, the underlying thermochemical properties are not well understood that would allow prediction of equilibrium conditions and driving forces. In addition, obtaining accurate values for the energetics of metal sulfide systems is far from complete, suggesting application of density functional theory (DFT) calculations. Here, the results of an examination of 69 phases by DFT using 12 exchange-correlation (X-C) functionals indicate that (i) the key source of error in predicting the Gibbs energy of a phase is the enthalpy calculated at 0 K rather than entropy at finite temperatures from phonon calculations and (ii) an improved prediction of the thermodynamic properties at 0 K relies on the selected nonlocal X-C functional such as the hybrid potential. Regarding metal sulfides, we conclude from the present DFT results that (1) the secondary phase Cu2ZnSn3S8, associated with the desired photovoltaic material Cu2ZnSnS4, is not stable at 0 K, but it becomes slightly stable with increasing temperature (i.e., >800 K), primarily due to the vibrational entropy, which makes it difficult to be detected in a typical thin-film growth process; (2) the hybrid X-C functional improves the predicted energetics for most of the layered transition-metal disulfides such as TiS2, MoS2, and WS2, but not for the nonlayered RuS2, OsS2, and IrS2 as well as the layered PdS2; and (3) the formation of the solid-state electrolyte Na3PS4 is thermodynamically favored. We further conclude that accurate energetics as a function of temperature for the materials of interest is feasible to be achieved beyond the semilocal DFT calculations with the key being enthalpy predicted at 0 K.

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U2 - 10.1103/PhysRevMaterials.3.015401

DO - 10.1103/PhysRevMaterials.3.015401

M3 - Article

VL - 3

JO - Physical Review Materials

JF - Physical Review Materials

SN - 2475-9953

IS - 1

M1 - 015401

ER -