Debye-Waller factors (DWFs) of metallic Cu (fcc crystal) in X-ray absorption fine structure (XAFS) presented in terms of cumulant expansion have been studied based on the anharmonic correlated Debye model (ACDM). This ACDM is derived from the many-body perturbation approach and the anharmonic effective potential that includes the first shell near neighbor contributions to the vibration between absorber and backscatterer atoms. | VNU Journal of Science: Mathematics – Physics, Vol. 33, No. 3 (2017) 36-43 Anharmonic Correlated Debye Model Debye-Waller Factors of Metallic Copper Compared to Experiment and to Other Theories Nguyen Van Hung1,*, Nguyen Bao Trung1, Nguyen Cong Toan1, Ha Dang Khoa2 Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Hanoi, Vietnam 2 School of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet, Hanoi, Vietnam Received 15 March 2017 Revised 27 April 2017; Accepted 19 September 2017 Abstract: Debye-Waller factors (DWFs) of metallic Cu (fcc crystal) in X-ray absorption fine structure (XAFS) presented in terms of cumulant expansion have been studied based on the anharmonic correlated Debye model (ACDM). This ACDM is derived from the many-body perturbation approach and the anharmonic effective potential that includes the first shell near neighbor contributions to the vibration between absorber and backscatterer atoms. Analytical expressions of three first XAFS cumulants of Cu have been derived involving more information of phonon-phonon interactions taken from integration over the first Brillouin zone. Morse potential is assumed to describe the single-pair atomic interaction. Numerical results for Cu using the present ACDM show their good agreement with experiment and with those of other theories, as well as their advantages compared to those calculated using the single-pair potential. Keywords: Debye-Waller factor, XAFS cumulants, effective potential, correlated Debye model, metallic Cu. 1. Introduction X-ray absorption fine structure (XAFS) has developed into a powerful probe of atomic structure and thermal effects of substances. XAFS expression contains Debye-Waller factor (DWF) presented in terms of cumulant expansion, where the first cumulant describes the net thermal expansion, the second one describes the mean square relative displacement (MSRD), the third cumulant describes the anharmonic contribution to XAFS phase [1].
