TY - JOUR

T1 - Ab initio (DFT) calculations of corundum (α-Al 2 O 3 ) Oxygen isotope fractionation

AU - Krylov, Dmitry P.

AU - Evarestov, Robert A.

PY - 2018/12/20

Y1 - 2018/12/20

N2 - Equilibrium oxygen isotope ( 18 O/ 16 O) fractionations (β-factors) for corundum are predicted from first principles using the “frozen phonon” technique within the density functional theory (DFT). Calculations of the phonon frequencies and the isotopic frequency shifts were consequently performed over 1, 3, 8, and 27 wave vectors using the supercell approach, with the Gaussian-type all-electron basis sets and hybrid functional B3LYP. The presented phonon frequencies agree with experimental infra-red and Raman data. The results of β-factor calculations are presented in terms of the logarithmic functions, 1000lnβ crn , computed for temperatures from 0 to 2000 °C with a computational step of 20 °C and then fitted by the conventional cubic polynomial Ax + Bx 2 + Cx 3 , with x = 10 6 /T(K) 2 . The following expressions corrected for incomplete Brillouin-zone sampling quantify oxygen isotope fractionation of corundum. Within the harmonic approximation: 1000 ln β crn = 9.2657x - 0.12110x 2 + 0.00175x 3 (0 < T°C < 2000. Accounting for thermal expansion (the quasi-harmonic approximation): 1000 ln β crn = 9.03363 x - 0.08912x 2 + 0.00036 x 3 (0 < T °C < 1570 ) The pressure effect on corundum β-factors is found to be negligible below ca. 25 kbar at temperatures exceeding 500 °C. At ultra-high pressures the correction can be made using the expression (∂(1000lnβ)/∂P)T (kbar) = 0.00967 × 10 6 /T(K) 2 .

AB - Equilibrium oxygen isotope ( 18 O/ 16 O) fractionations (β-factors) for corundum are predicted from first principles using the “frozen phonon” technique within the density functional theory (DFT). Calculations of the phonon frequencies and the isotopic frequency shifts were consequently performed over 1, 3, 8, and 27 wave vectors using the supercell approach, with the Gaussian-type all-electron basis sets and hybrid functional B3LYP. The presented phonon frequencies agree with experimental infra-red and Raman data. The results of β-factor calculations are presented in terms of the logarithmic functions, 1000lnβ crn , computed for temperatures from 0 to 2000 °C with a computational step of 20 °C and then fitted by the conventional cubic polynomial Ax + Bx 2 + Cx 3 , with x = 10 6 /T(K) 2 . The following expressions corrected for incomplete Brillouin-zone sampling quantify oxygen isotope fractionation of corundum. Within the harmonic approximation: 1000 ln β crn = 9.2657x - 0.12110x 2 + 0.00175x 3 (0 < T°C < 2000. Accounting for thermal expansion (the quasi-harmonic approximation): 1000 ln β crn = 9.03363 x - 0.08912x 2 + 0.00036 x 3 (0 < T °C < 1570 ) The pressure effect on corundum β-factors is found to be negligible below ca. 25 kbar at temperatures exceeding 500 °C. At ultra-high pressures the correction can be made using the expression (∂(1000lnβ)/∂P)T (kbar) = 0.00967 × 10 6 /T(K) 2 .

KW - O/ O fractionation

KW - B-factors

KW - Corundum

KW - Density functional theory

KW - First principles

KW - Oxygen isotopes

UR - http://www.scopus.com/inward/record.url?scp=85058803481&partnerID=8YFLogxK

U2 - 10.1127/ejm/2018/0030-2786

DO - 10.1127/ejm/2018/0030-2786

M3 - Article

AN - SCOPUS:85058803481

VL - 30

SP - 1063

EP - 1070

JO - European Journal of Mineralogy

JF - European Journal of Mineralogy

SN - 0935-1221

IS - 6

ER -