Effect of the iron valence in the two types of layers in LiFeO2_2Fe2_2Se2_2

We perform electronic structure calculations for the recently synthesized iron-based superconductor LiFeO$_2$Fe$_2$Se$_2$. In contrast to other iron-based superconductors, this material comprises two different iron atoms in 3$d^5$ and 3$d^6$ configurations. In band theory, both contribute to the low-energy electronic structure. Spin-polarized density functional theory calculations predict an antiferromagnetic metallic ground state with different moments on the two Fe sites. However, several other almost degenerate magnetic configurations exist. Due to their different valences, the two iron atoms behave very differently when local quantum correlations are included through the dynamical mean-field theory. The contributions from the half-filled 3$d^5$ atoms in the LiFeO$_2$ layer are suppressed and the 3$d^6$ states from the FeSe layer restore the standard iron-based superconductor fermiology.Comment: 9 pages, 11 figure

Pattern transitions in diary data of MDD patients: a mixed-methods multiple case study of psychotherapy dynamics

AimMixed-methods approaches promise a deep understanding of psychotherapeutic processes. This study uses qualitative and quantitative data from daily diary entries and daily self-assessments during inpatient treatment. The aim of the study is to get an insight into the similarities and differences between both types of data and how they represent self-organized pattern transitions in psychotherapy. While a complete correlation of results is not expected, we anticipate observing amplifying and subsidiary patterns from both perspectives.Materials and methodsDaily, five MDD patients wrote diaries and completed self-assessments using the Therapy Process Questionnaire, a questionnaire for monitoring the change dynamics of psychotherapy. The data were collected using the Synergetic Navigation System, an online tool for real-time monitoring. Diary entries of the patients described their experiences in everyday life. The qualitative text analysis was conducted using Mixed Grounded Theory, which provided categories representing the patients’ ongoing experiences of transformation and stagnation. The time series data was analyzed using the dynamic complexity algorithm and the pattern transition detection algorithm. Results from qualitative and quantitative analyses were combined and compared. Following the process of data triangulation, the leading perspective came from the theory of self-organization. In addition to presenting the overall results for all five patients, we delve into two specific case examples in greater detail.ResultsSpecific and highly diversified diary entries of 5 patients were classified into the categories of perceived pattern stability, noticing improvement, broadening the perspective, critical instability, and experiencing moments of Kairos. Patients reported problems not only related to their disorder (e.g., lack of energy and hopelessness) but also to phases and steps of change, which could be related to the theory of self-organization (e.g., problem attractors, critical fluctuations, pattern transitions, and Kairos). Qualitative and quantitative analysis provide important supplementary results without being redundant or identical.ConclusionData triangulation allows for a comprehensive and multi-perspective understanding of therapeutic change dynamics. The different topics expressed in the diary entries especially help to follow micro-psychological processes, which are far from being a simple reaction to interventions. The way patients experience themselves being in stability or instability and stagnation or transformation is surprisingly close to the general features of self-organizing processes in complex systems

Accurate bare susceptibilities from full-potential ab initio\textit{ab initio} calculations

Electronic susceptibilities are a very popular tool to study electronic and magnetic properties of materials, both in experiment and theory. Unfortunately, the numerical evaluation of even the bare susceptibility, which depends on the computation of matrix elements and sums over energy bands, is very work-intensive and therefore various approximations have been introduced to speed up the calculations. We present a reliable and efficient implementation to compute static as well as dynamic bare susceptibilities based on full-potential density functional theory (DFT) calculations. Based on the exact results we will assess the accuracy of replacing the matrix elements with a constant and the impact of truncating the sum over the energy bands. Results will be given for representative and topical materials, such as Cr, a classical transition metal, as well as for FeSe and LaFeAsO, examples of iron-based superconductors.Comment: 10 pages, 10 figure

Brain Oscillatory Correlates of Altered Executive Functioning in Positive and Negative Symptomatic Schizophrenia Patients and Healthy Controls

Working Memory and executive functioning deficits are core characteristics of patients suffering from schizophrenia. Electrophysiological research indicates that altered patterns of neural oscillatory mechanisms underpinning executive functioning are associated with the psychiatric disorder. Such brain oscillatory changes have been found in local amplitude differences at gamma and theta frequencies in task-specific cortical areas. Moreover, interregional interactions are also disrupted as signified by decreased phase coherence of fronto-posterior theta activity in schizophrenia patients. However, schizophrenia is not a one-dimensional psychiatric disorder but has various forms and expressions. A common distinction is between positive and negative symptomatology but most patients have both negative and positive symptoms to some extent. Here, we examined three groups – healthy controls, predominantly negative and predominantly positive symptomatic schizophrenia patients – when performing a working memory task with increasing cognitive demand and increasing need for executive control. We analysed brain oscillatory activity in the three groups separately and investigated how predominant symptomatology might explain differences in brain oscillatory patterns. Our results indicate that differences in task specific fronto-posterior network activity (i.e. executive control network) expressed by interregional phase synchronisation are able to account for working memory dysfunctions between groups. Local changes in the theta and gamma frequency range also show differences between patients and healthy controls, and more importantly, between the two patient groups. We conclude that differences in oscillatory brain activation patterns related to executive processing can be an indicator for positive and negative symptomatology in schizophrenia. Furthermore, changes in cognitive and especially executive functioning in patients are expressed by alterations in a task-specific fronto-posterior connectivity even in the absence of behavioural impairment

Polaritonic properties of the Jaynes-Cummings lattice model in two dimensions

Light-matter systems allow to realize a strongly correlated phase where photons are present. In these systems strong correlations are achieved by optical nonlinearities, which appear due to the coupling of photons to atomic-like structures. This leads to intriguing effects, such as the quantum phase transition from the Mott to the superfluid phase. Here, we address the two-dimensional Jaynes-Cummings lattice model. We evaluate the boundary of the quantum phase transition and study polaritonic properties. In order to be able to characterize polaritons, we investigate the spectral properties of both photons as well as two-level excitations. Based on this information we introduce polariton quasiparticles as appropriate wavevector, band index, and filling dependent superpositions of photons and two-level excitations. Finally, we analyze the contributions of the individual constituents to the polariton quasiparticles.Comment: 5 pages, 4 figures, Proceedings of the Conference on Computational Physics CCP, June 2010, Trondheim, Norwa

Loss, gain and choice difficulty in gambling patients: Neural and behavioural processes

Impaired decision‐making is often displayed by individuals suffering from gambling disorder (GD). Since there are a variety of different phenomena influencing decision‐making, we focused in this study on the effects of GD on neural and behavioural processes related to loss aversion and choice difficulty. Behavioural responses as well as brain images of 23 patients with GD and 20 controls were recorded while they completed a mixed gambles task, where they had to decide to either accept or reject gambles with different amounts of potential gain and loss. We found no behavioural loss aversion in either group and no group differences regarding loss and gain‐related choice behaviour, but there was a weaker relation between choice difficulty and decision time in patients with GD. Similarly, we observed no group differences in processing of losses or gains, but choice difficulty was weaker associated with brain activity in the right anterior insula and anterior cingulate cortex in patients with GD. Our results showed for the first time the effects of GD on neural processes related to choice difficulty. In addition, our findings on choice difficulty give new insights on the psychopathology of GD and on neural processes related to impaired decision‐making in GD