Laplacian-level meta-generalized gradient approximation for solid and liquid metals

We derive and motivate a Laplacian-level, orbital-free meta-generalized-gradient approximation (LL-MGGA) for the exchange-correlation energy, targeting accurate ground-state properties of $sp$ and $sd$ metallic condensed matter, in which the density functional for the exchange-correlation energy is only weakly nonlocal due to perfect long-range screening. Our model for the orbital-free kinetic energy density restores the fourth-order gradient expansion for exchange to the r$^2$SCAN meta-GGA [Furness et al., J. Phys. Chem. Lett. 11, 8208 (2020)], yielding a LL-MGGA we call OFR2. OFR2 matches the accuracy of SCAN for prediction of common lattice constants and improves the equilibrium properties of alkali metals, transition metals, and intermetallics that were degraded relative to the PBE GGA values by both SCAN and r$^2$SCAN. We compare OFR2 to the r$^2$SCAN-L LL-MGGA [D. Mejia-Rodriguez and S.B. Trickey, Phys. Rev. B 102, 121109 (2020)] and show that OFR2 tends to outperform r$^2$SCAN-L for the equilibrium properties of solids, but r$^2$SCAN-L much better describes the atomization energies of molecules than OFR2 does. For best accuracy in molecules and non-metallic condensed matter, we continue to recommend SCAN and r$^2$SCAN. Numerical performance is discussed in detail, and our work provides an outlook to machine learning.Comment: Significant revisions in response to referee comments. Under review at Physical Review Material

Classical turning surfaces in solids: When do they occur, and what do they mean?

Classical turning surfaces of Kohn-Sham potentials, separating classically-allowed regions (CARs) from classically-forbidden regions (CFRs), provide a useful and rigorous approach to understanding many chemical properties of molecules. Here we calculate such surfaces for several paradigmatic solids. Our study of perfect crystals at equilibrium geometries suggests that CFRs are absent in metals, rare in covalent semiconductors, but common in ionic and molecular crystals. A CFR can appear at a monovacancy in a metal. In all materials, CFRs appear or grow as the internuclear distances are uniformly expanded. Calculations with several approximate density functionals and codes confirm these behaviors. A classical picture of conduction suggests that CARs should be connected in metals, and disconnected in wide-gap insulators. This classical picture is confirmed in the limits of extreme uniform compression of the internuclear distances, where all materials become metals without CFRs, and extreme expansion, where all materials become insulators with disconnected and widely-separated CARs around the atoms.Comment: Added supplemental information (63 pages), was missing in original submission. Minor typo corrections in Tables I and III for Eps_HO - vs(r) column (and CFR % volume for Pt monovacancy) for PBE data onl

Patterns of Senescence in Human Cardiovascular Fitness: Vo2 Max in Subsistence and Industrialized Populations

Objectives—This study explores whether cardiovascular fitness levels and senescent decline are similar in the Tsimane of Bolivia and Canadians, as well as other subsistence and industrialized populations. Among Tsimane, we examine whether morbidity predicts lower levels and faster decline of cardiovascular fitness, or whether their lifestyle (e.g., high physical activity) promotes high levels and slow decline. Alternatively, high activity levels and morbidity might counterbalance such that Tsimane fitness levels and decline are similar to those in industrialized populations. Methods—Maximal oxygen uptake (VO2max) was estimated using a step test heart rate method for 701 participants. We compared these estimates to the Canadian Health Measures Survey and previous studies in industrialized and subsistence populations. We evaluated whether health indicators and proxies for market integration were associated with VO2max levels and rate of decline for the Tsimane. Results—The Tsimane have significantly higher levels of VO2max and slower rates of decline than Canadians; initial evidence suggests differences in VO2max levels between other subsistence and industrialized populations. Low hemoglobin predicts low VO2max for Tsimane women while helminth infection predicts high VO2max for Tsimane men, though results might be specific to the VO2max scaling parameter used. No variables tested interact with age to moderate decline. Conclusions—The Tsimane demonstrate higher levels of cardiovascular fitness than industrialized populations, but levels similar to other subsistence populations. The high VO2max of Tsimane is consistent with their high physical activity and few indicators of cardiovascular disease, measured in previous studies

Frame-Dragging Vortexes and Tidal Tendexes Attached to Colliding Black Holes: Visualizing the Curvature of Spacetime

When one splits spacetime into space plus time, the spacetime curvature (Weyl tensor) gets split into an "electric" part E_{jk} that describes tidal gravity and a "magnetic" part B_{jk} that describes differential dragging of inertial frames. We introduce tools for visualizing B_{jk} (frame-drag vortex lines, their vorticity, and vortexes) and E_{jk} (tidal tendex lines, their tendicity, and tendexes), and also visualizations of a black-hole horizon's (scalar) vorticity and tendicity. We use these tools to elucidate the nonlinear dynamics of curved spacetime in merging black-hole binaries.Comment: 4 pages, 5 figure

Depression as Sickness Behavior? A Test of the Host Defense Hypothesis in a High Pathogen Population

Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter “depression”) have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. “sickness behavior”) that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian foragerhorticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions

Modernization, Sexual Risk-Taking, and Gynecological Morbidity Among Bolivian Forager-Horticulturalists

Sexual risk-taking and reproductive morbidity are common among rapidly modernizing populations with little material wealth, limited schooling, minimal access to modern contraception and healthcare, and gendered inequalities in resource access that limit female autonomy in cohabiting relationships. Few studies have examined how modernization influences sexual risk-taking and reproductive health early in demographic transition. Tsimane are a natural fertility population of Bolivian forager-farmers; they are not urbanized, reside in small-scale villages, and lack public health infrastructure. We test whether modernization is associated with greater sexual risk-taking, report prevalence of gynecological morbidity (GM), and test whether modernization, sexual risk-taking and parity are associated with greater risk of GM. Data were collected from 2002–2010 using interviews, clinical exams, and laboratory analysis of cervical cells. We find opposing effects of modernization on both sexual risk-taking and risk of GM. Residential proximity to town and Spanish fluency are associated with greater likelihood of men’s infidelity, and with number of lifetime sexual partners for men and women. However, for women, literacy is associated with delayed sexual debut after controlling for town proximity. Fifty-five percent of women present at least one clinical indicator of GM (n = 377); 48% present inflammation of cervical cells, and in 11% the inflammation results from sexually transmitted infection (trichomoniasis). Despite having easier access to modern healthcare, women residing near town experience greater likelihood of cervical inflammation and trichomoniasis relative to women in remote villages; women who are fluent in Spanish are also more likely to present trichomoniasis relative to women with moderate or no fluency. However, literate women experience lower likelihood of trichomoniasis. Parity has no effect on risk of GM. Our results suggest a net increase in risk of reproductive morbidity among rapidly modernizing, resource-stressed populations

Cardiovascular Disease and Type 2 Diabetes in Evolutionary Perspective: A Critical Role for Helminths?

Heart disease and type 2 diabetes are commonly believed to be rare among contemporary subsistencelevel human populations, and by extension prehistoric populations. Although some caveats remain, evidence shows these diseases to be unusual among well-studied hunter-gatherers and other subsistence populations with minimal access to healthcare. Here we expand on a relatively new proposal for why these and other populations may not show major signs of these diseases. Chronic infections, especially helminths, may offer protection against heart disease and diabetes through direct and indirect pathways. As part of a strategy to insure their own survival and reproduction, helminths exert multiple cardio-protective effects on their host through their effects on immune function and blood lipid metabolism. Helminths consume blood lipids and glucose, alter lipid metabolism, and modulate immune function towards Th-2 polarization—which combined can lower blood cholesterol, reduce obesity, increase insulin sensitivity, decrease atheroma progression, and reduce likelihood of atherosclerotic plaque rupture. Traditional cardiometabolic risk factors, coupled with the mismatch between our evolved immune systems and modern, hygienic environments may interact in complex ways. In this review, we survey existing studies in the non-human animal and human literature, highlight unresolved questions and suggest future directions to explore the role of helminths in the etiology of cardio-metabolic disease

Methodological Differences Cannot Explain Associations Between Health, Anthropometrics, and Excess Resting Metabolic Rate

We appreciate Ocobock\u27s interest in methodological rigor. We largely agree with her commentary, which suggests that departures from standard protocols might have contributed to the high resting metabolic rate (RMR) measured for Tsimane. Indeed, our paper acknowledges many of the key departures from gold-standard indirect calorimetry methods of RMR assessment and attempts to adjust for several of these (Gurven et al., 2016). Bringing standard clinical methods into remote field settings often involves certain compromises, especially in our case, where RMR measurement was just one component of a large-scale health and aging project (Gurven et al., 2017). RMR data collection was from 2012 to 2014, and where we to measure RMR again for focused follow up, we would consider new available technologies, improve our protocol to the extent possible, and compare against our published estimates

Symmetry Breaking with the SCAN Density Functional Describes Strong Correlation in the Singlet Carbon Dimer

The SCAN (strongly constrained and appropriately normed) meta-generalized gradient approximation (meta-GGA), which satisfies all 17 exact constraints that a meta-GGA can satisfy, accurately describes equilibrium bonds that are normally correlated. With symmetry breaking, it also accurately describes some sd equilibrium bonds that are strongly correlated. While sp equilibrium bonds are nearly always normally correlated, the C2 singlet ground state is known to be a rare case of strong correlation in an sp equilibrium bond. Earlier work that calculated atomization energies of the molecular sequence B2, C2, O2, and F2 in the local spin density approximation (LSDA), the Perdew-Burke-Ernzerhof (PBE) GGA, and the SCAN meta-GGA, without symmetry breaking in the molecule, found that only SCAN was accurate enough to reveal an anomalous under-binding for C2. This work shows that spin symmetry breaking in singlet C2, the appearance of net up- and down-spin densities on opposite sides (not ends) of the bond, corrects that under-binding, with a small SCAN atomization-energy error more like that of the other three molecules, suggesting that symmetry-breaking with an advanced density functional might reliably describe strong correlation. This article also discusses some general aspects of symmetry breaking, and the insights into strong correlation that symmetry-breaking can bring.Comment: 10 pages, 3 figures, 1 Tabl