First-principles X-ray absorption dose calculation for time-dependent mass and optical density

2018 ◽  
Vol 25 (3) ◽  
pp. 833-847 ◽  
Author(s):  
Viatcheslav Berejnov ◽  
Boris Rubinstein ◽  
Lis G. A. Melo ◽  
Adam P. Hitchcock

A dose integral of time-dependent X-ray absorption under conditions of variable photon energy and changing sample mass is derived from first principles starting with the Beer–Lambert (BL) absorption model. For a given photon energy the BL dose integralD(e, t) reduces to the product of an effective time integralT(t) and a dose rateR(e). Two approximations of the time-dependent optical density,i.e.exponentialA(t) =c+aexp(−bt) for first-order kinetics and hyperbolicA(t) =c+a/(b+t) for second-order kinetics, were considered for BL dose evaluation. For both models three methods of evaluating the effective time integral are considered: analytical integration, approximation by a function, and calculation of the asymptotic behaviour at large times. Data for poly(methyl methacrylate) and perfluorosulfonic acid polymers measured by scanning transmission soft X-ray microscopy were used to test the BL dose calculation. It was found that a previous method to calculate time-dependent dose underestimates the dose in mass loss situations, depending on the applied exposure time. All these methods here show that the BL dose is proportional to the exposure timeD(e, t) ≃K(e)t.

2016 ◽  
Vol 18 (1) ◽  
pp. 566-583 ◽  
Author(s):  
Thomas Fransson ◽  
Iurii Zhovtobriukh ◽  
Sonia Coriani ◽  
Kjartan T. Wikfeldt ◽  
Patrick Norman ◽  
...  

Transition-potential and time-dependent density functional theory XAS calculations are presented for water and ice, showing excellent agreement between TDDFT results and experimental spectra.


2014 ◽  
Vol 52 (12) ◽  
pp. 1025-1029
Author(s):  
Min-Wook Oh ◽  
Tae-Gu Kang ◽  
Byungki Ryu ◽  
Ji Eun Lee ◽  
Sung-Jae Joo ◽  
...  

2010 ◽  
Vol 82 (15) ◽  
Author(s):  
Weijie Hua ◽  
Bin Gao ◽  
Shuhua Li ◽  
Hans Ågren ◽  
Yi Luo

2014 ◽  
Vol 118 (47) ◽  
pp. 27210-27218 ◽  
Author(s):  
Marcus Fehse ◽  
Mouna Ben Yahia ◽  
Laure Monconduit ◽  
Frédéric Lemoigno ◽  
Marie-Liesse Doublet ◽  
...  

2020 ◽  
Vol 31 (08) ◽  
pp. 2050109
Author(s):  
S. Uba ◽  
A. Bonda ◽  
L. Uba ◽  
L. V. Bekenov ◽  
V. N. Antonov

Electronic structure, X-ray absorption, and magnetic circular dichroism (XMCD) spectra in the CoFeMnSi Heusler alloy were studied from first principles. Fully relativistic Dirac linear muffin-tin orbital band structure method was implemented with various exchange–correlation functionals tested. The supercell approach was used to study the influence of intersite disorder, at the levels of 6.25%, 12.5%, and 25% within transition metal sites, on the XMCD spectra at [Formula: see text] edges and spin polarization (SP) at the Fermi level. It is found that most sensitive to Fe–Mn and Co–Fe disorder are XMCD spectra at [Formula: see text] edges of Fe, while the sensitivity decreases from Mn to Co. It is shown that magnetic moments estimated with the use of magneto-optical (MO) sum rules agree with the ab initio calculated ones to within [Formula: see text], [Formula: see text], and [Formula: see text], for Co, Fe, and Mn, respectively. The calculated SP decreases from 99% for ordered CoFeMnSi alloy, to 96% upon 25% Co–Fe disorder, to 83% for Fe–Mn disorder, and to 42% in the case of Co–Mn disorder. The calculated spectra agree well with the available experimental data. The rich XMCD spectral structures are predicted from first principles at Fe, Co, Mn and Si [Formula: see text] edges.


Sign in / Sign up

Export Citation Format

Share Document