ABSTRACT
In this work, we explore the relative accuracy to which a hybrid functional, in the context of density functional theory, may predict redox properties under the constraint of satisfying the general form of Koopmans' theorem. Taking aqueous iron as our model system within the framework of first-principles molecular dynamics, direct comparison between computed single-particle energies and experimental ionization data is assessed by both (1) tuning the degree of hybrid exchange, to satisfy the general form of Koopmans' theorem, and (2) ensuring the application of finite-size corrections. These finite-size corrections are benchmarked through classical molecular dynamics calculations, extended to large atomic ensembles, for which good convergence is obtained in the large supercell limit. Our first-principles findings indicate that while precise quantitative agreement with experimental ionization data cannot always be attained for solvated systems, when satisfying the general form of Koopmans' theorem via hybrid functionals, theoretically robust estimates of single-particle redox energies are most often arrived at by employing a total energy difference approach. That is, when seeking to employ a value of exact exchange that does not satisfy the general form of Koopmans' theorem, but some other physical metric, the single-particle energy estimate that would most closely align with the general form of Koopmans' theorem is obtained from a total energy difference approach. In this respect, these findings provide important guidance for the more general comparison of redox energies computed via hybrid functionals with experimental data.
ABSTRACT
Perovskites are widely utilized either as a primary component or as a substrate in which the dynamics of charged oxygen vacancy defects play an important role. Current knowledge regarding the dynamics of vacancy mobility in perovskites is solely based upon volume- and/or time-averaged measurements. This impedes our understanding of the basic physical principles governing defect migration in inorganic materials. Here, we measure the ergodic and nonergodic dynamics of vacancy migration at the relevant spatial and temporal scales using time-resolved atomic force microscopy techniques. Our findings demonstrate that the time constant associated with oxygen vacancy migration is a local property and can change drastically on short length and time scales, such that nonergodic states lead to a dramatic increase in the migration barrier. This correlated spatial and temporal variation in oxygen vacancy dynamics can extend hundreds of nanometers across the surface in inorganic perovskites.
ABSTRACT
BACKGROUND: Cholangiocarcinoma is an invasive biliary malignancy with poor prognosis. Diagnostic accuracy of conventional methods is low which is mainly due to the specific anatomy of the disease. The aim of this study was to evaluate the diagnostic value of biochemical profile and tumor marker of the bile in patients with malignant cholestasis compared to that of choledocholithiasis. METHODS: In this cross-sectional study, 46 patients with extrahepatic cholestasis were enrolled (20 patients with malignant cholestasis and 26 patients with choledocolithiasis) A definitive diagnosis of cholangiocarcinoma was made by imaging, cytology and biopsy. Bile fluid was obtained by aspiration through endoscopic retrograde cholagiopantreatography (ERCP) catheter or percutaneous drainage in patients with choledocolithiasis and cholangiocarcinoma respectively. Sex and age were matched in two groups. Data regarding the biochemical profile (triglyceride, (TG), cholesterol, billirubin and HDL) and CA19.9 level of the bile fluid were collected, then using the SPSS software, the data were analyzed. RESULTS: Bile fluid level of TG, cholesterol, high - density lipoprotein (HDL), direct bilirubin and CA19.9 were significantly higher in patients with benign cholestasis in comparison with malignant cholestasis (P<0.001, P<0.001, P<0.001, P=0.012 and P= 0.03, respectively). CONCLUSION: Our study showed that the CA19.9 level of bile fluid in extrahepatic cholestasis due to biliary stone was significantly higher than those with cholangiocarcinoma, as is the biliary level of TG, cholesterol, high-density lipoprotein (HDL) and direct bilirubin. Thus they may help in the differentiation of benign versus malignant extra hepatic cholestasis.
