Global incidence, prevalence, years lived with disability (YLDs), disability-adjusted life-years (DALYs), and healthy life expectancy (HALE) for 371 diseases and injuries in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Detailed, comprehensive, and timely reporting on population health by underlying causes of disability and premature death is crucial to understanding and responding to complex patterns of disease and injury burden over time and across age groups, sexes, and locations. The availability of disease burden estimates can promote evidence-based interventions that enable public health researchers, policy makers, and other professionals to implement strategies that can mitigate diseases. It can also facilitate more rigorous monitoring of progress towards national and international health targets, such as the Sustainable Development Goals. For three decades, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) has filled that need. A global network of collaborators contributed to the production of GBD 2021 by providing, reviewing, and analysing all available data. GBD estimates are updated routinely with additional data and refined analytical methods. GBD 2021 presents, for the first time, estimates of health loss due to the COVID-19 pandemic. Methods: The GBD 2021 disease and injury burden analysis estimated years lived with disability (YLDs), years of life lost (YLLs), disability-adjusted life-years (DALYs), and healthy life expectancy (HALE) for 371 diseases and injuries using 100 983 data sources. Data were extracted from vital registration systems, verbal autopsies, censuses, household surveys, disease-specific registries, health service contact data, and other sources. YLDs were calculated by multiplying cause-age-sex-location-year-specific prevalence of sequelae by their respective disability weights, for each disease and injury. YLLs were calculated by multiplying cause-age-sex-location-year-specific deaths by the standard life expectancy at the age that death occurred. DALYs were calculated by summing YLDs and YLLs. HALE estimates were produced using YLDs per capita and age-specific mortality rates by location, age, sex, year, and cause. 95% uncertainty intervals (UIs) were generated for all final estimates as the 2·5th and 97·5th percentiles values of 500 draws. Uncertainty was propagated at each step of the estimation process. Counts and age-standardised rates were calculated globally, for seven super-regions, 21 regions, 204 countries and territories (including 21 countries with subnational locations), and 811 subnational locations, from 1990 to 2021. Here we report data for 2010 to 2021 to highlight trends in disease burden over the past decade and through the first 2 years of the COVID-19 pandemic. Findings: Global DALYs increased from 2·63 billion (95% UI 2·44–2·85) in 2010 to 2·88 billion (2·64–3·15) in 2021 for all causes combined. Much of this increase in the number of DALYs was due to population growth and ageing, as indicated by a decrease in global age-standardised all-cause DALY rates of 14·2% (95% UI 10·7–17·3) between 2010 and 2019. Notably, however, this decrease in rates reversed during the first 2 years of the COVID-19 pandemic, with increases in global age-standardised all-cause DALY rates since 2019 of 4·1% (1·8–6·3) in 2020 and 7·2% (4·7–10·0) in 2021. In 2021, COVID-19 was the leading cause of DALYs globally (212·0 million [198·0–234·5] DALYs), followed by ischaemic heart disease (188·3 million [176·7–198·3]), neonatal disorders (186·3 million [162·3–214·9]), and stroke (160·4 million [148·0–171·7]). However, notable health gains were seen among other leading communicable, maternal, neonatal, and nutritional (CMNN) diseases. Globally between 2010 and 2021, the age-standardised DALY rates for HIV/AIDS decreased by 47·8% (43·3–51·7) and for diarrhoeal diseases decreased by 47·0% (39·9–52·9). Non-communicable diseases contributed 1·73 billion (95% UI 1·54–1·94) DALYs in 2021, with a decrease in age-standardised DALY rates since 2010 of 6·4% (95% UI 3·5–9·5). Between 2010 and 2021, among the 25 leading Level 3 causes, age-standardised DALY rates increased most substantially for anxiety disorders (16·7% [14·0–19·8]), depressive disorders (16·4% [11·9–21·3]), and diabetes (14·0% [10·0–17·4]). Age-standardised DALY rates due to injuries decreased globally by 24·0% (20·7–27·2) between 2010 and 2021, although improvements were not uniform across locations, ages, and sexes. Globally, HALE at birth improved slightly, from 61·3 years (58·6–63·6) in 2010 to 62·2 years (59·4–64·7) in 2021. However, despite this overall increase, HALE decreased by 2·2% (1·6–2·9) between 2019 and 2021. Interpretation: Putting the COVID-19 pandemic in the context of a mutually exclusive and collectively exhaustive list of causes of health loss is crucial to understanding its impact and ensuring that health funding and policy address needs at both local and global levels through cost-effective and evidence-based interventions. A global epidemiological transition remains underway. Our findings suggest that prioritising non-communicable disease prevention and treatment policies, as well as strengthening health systems, continues to be crucially important. The progress on reducing the burden of CMNN diseases must not stall; although global trends are improving, the burden of CMNN diseases remains unacceptably high. Evidence-based interventions will help save the lives of young children and mothers and improve the overall health and economic conditions of societies across the world. Governments and multilateral organisations should prioritise pandemic preparedness planning alongside efforts to reduce the burden of diseases and injuries that will strain resources in the coming decades. Funding: Bill & Melinda Gates Foundation

Global burden and strength of evidence for 88 risk factors in 204 countries and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Understanding the health consequences associated with exposure to risk factors is necessary to inform public health policy and practice. To systematically quantify the contributions of risk factor exposures to specific health outcomes, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 aims to provide comprehensive estimates of exposure levels, relative health risks, and attributable burden of disease for 88 risk factors in 204 countries and territories and 811 subnational locations, from 1990 to 2021. Methods: The GBD 2021 risk factor analysis used data from 54 561 total distinct sources to produce epidemiological estimates for 88 risk factors and their associated health outcomes for a total of 631 risk–outcome pairs. Pairs were included on the basis of data-driven determination of a risk–outcome association. Age-sex-location-year-specific estimates were generated at global, regional, and national levels. Our approach followed the comparative risk assessment framework predicated on a causal web of hierarchically organised, potentially combinative, modifiable risks. Relative risks (RRs) of a given outcome occurring as a function of risk factor exposure were estimated separately for each risk–outcome pair, and summary exposure values (SEVs), representing risk-weighted exposure prevalence, and theoretical minimum risk exposure levels (TMRELs) were estimated for each risk factor. These estimates were used to calculate the population attributable fraction (PAF; ie, the proportional change in health risk that would occur if exposure to a risk factor were reduced to the TMREL). The product of PAFs and disease burden associated with a given outcome, measured in disability-adjusted life-years (DALYs), yielded measures of attributable burden (ie, the proportion of total disease burden attributable to a particular risk factor or combination of risk factors). Adjustments for mediation were applied to account for relationships involving risk factors that act indirectly on outcomes via intermediate risks. Attributable burden estimates were stratified by Socio-demographic Index (SDI) quintile and presented as counts, age-standardised rates, and rankings. To complement estimates of RR and attributable burden, newly developed burden of proof risk function (BPRF) methods were applied to yield supplementary, conservative interpretations of risk–outcome associations based on the consistency of underlying evidence, accounting for unexplained heterogeneity between input data from different studies. Estimates reported represent the mean value across 500 draws from the estimate's distribution, with 95% uncertainty intervals (UIs) calculated as the 2·5th and 97·5th percentile values across the draws. Findings: Among the specific risk factors analysed for this study, particulate matter air pollution was the leading contributor to the global disease burden in 2021, contributing 8·0% (95% UI 6·7–9·4) of total DALYs, followed by high systolic blood pressure (SBP; 7·8% [6·4–9·2]), smoking (5·7% [4·7–6·8]), low birthweight and short gestation (5·6% [4·8–6·3]), and high fasting plasma glucose (FPG; 5·4% [4·8–6·0]). For younger demographics (ie, those aged 0–4 years and 5–14 years), risks such as low birthweight and short gestation and unsafe water, sanitation, and handwashing (WaSH) were among the leading risk factors, while for older age groups, metabolic risks such as high SBP, high body-mass index (BMI), high FPG, and high LDL cholesterol had a greater impact. From 2000 to 2021, there was an observable shift in global health challenges, marked by a decline in the number of all-age DALYs broadly attributable to behavioural risks (decrease of 20·7% [13·9–27·7]) and environmental and occupational risks (decrease of 22·0% [15·5–28·8]), coupled with a 49·4% (42·3–56·9) increase in DALYs attributable to metabolic risks, all reflecting ageing populations and changing lifestyles on a global scale. Age-standardised global DALY rates attributable to high BMI and high FPG rose considerably (15·7% [9·9–21·7] for high BMI and 7·9% [3·3–12·9] for high FPG) over this period, with exposure to these risks increasing annually at rates of 1·8% (1·6–1·9) for high BMI and 1·3% (1·1–1·5) for high FPG. By contrast, the global risk-attributable burden and exposure to many other risk factors declined, notably for risks such as child growth failure and unsafe water source, with age-standardised attributable DALYs decreasing by 71·5% (64·4–78·8) for child growth failure and 66·3% (60·2–72·0) for unsafe water source. We separated risk factors into three groups according to trajectory over time: those with a decreasing attributable burden, due largely to declining risk exposure (eg, diet high in trans-fat and household air pollution) but also to proportionally smaller child and youth populations (eg, child and maternal malnutrition); those for which the burden increased moderately in spite of declining risk exposure, due largely to population ageing (eg, smoking); and those for which the burden increased considerably due to both increasing risk exposure and population ageing (eg, ambient particulate matter air pollution, high BMI, high FPG, and high SBP). Interpretation: Substantial progress has been made in reducing the global disease burden attributable to a range of risk factors, particularly those related to maternal and child health, WaSH, and household air pollution. Maintaining efforts to minimise the impact of these risk factors, especially in low SDI locations, is necessary to sustain progress. Successes in moderating the smoking-related burden by reducing risk exposure highlight the need to advance policies that reduce exposure to other leading risk factors such as ambient particulate matter air pollution and high SBP. Troubling increases in high FPG, high BMI, and other risk factors related to obesity and metabolic syndrome indicate an urgent need to identify and implement interventions

Burden of non-communicable diseases among adolescents aged 10–24 years in the EU, 1990–2019: a systematic analysis of the Global Burden of Diseases Study 2019

Background Disability and mortality burden of non-communicable diseases (NCDs) have risen worldwide; however, the NCD burden among adolescents remains poorly described in the EU. Methods Estimates were retrieved from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. Causes of NCDs were analysed at three different levels of the GBD 2019 hierarchy, for which mortality, years of life lost (YLLs), years lived with disability (YLDs), and disability-adjusted life-years (DALYs) were extracted. Estimates, with the 95% uncertainty intervals (UI), were retrieved for EU Member States from 1990 to 2019, three age subgroups (10–14 years, 15–19 years, and 20–24 years), and by sex. Spearman's correlation was conducted between DALY rates for NCDs and the Socio-demographic Index (SDI) of each EU Member State. Findings In 2019, NCDs accounted for 86·4% (95% uncertainty interval 83·5–88·8) of all YLDs and 38·8% (37·4–39·8) of total deaths in adolescents aged 10–24 years. For NCDs in this age group, neoplasms were the leading causes of both mortality (4·01 [95% uncertainty interval 3·62–4·25] per 100 000 population) and YLLs (281·78 [254·25–298·92] per 100 000 population), whereas mental disorders were the leading cause for YLDs (2039·36 [1432·56–2773·47] per 100 000 population) and DALYs (2040·59 [1433·96–2774·62] per 100 000 population) in all EU Member States, and in all studied age groups. In 2019, among adolescents aged 10–24 years, males had a higher mortality rate per 100 000 population due to NCDs than females (11·66 [11·04–12·28] vs 7·89 [7·53–8·23]), whereas females presented a higher DALY rate per 100 000 population due to NCDs (8003·25 [5812·78–10 701·59] vs 6083·91 [4576·63–7857·92]). From 1990 to 2019, mortality rate due to NCDs in adolescents aged 10–24 years substantially decreased (–40·41% [–43·00 to –37·61), and also the YLL rate considerably decreased (–40·56% [–43·16 to –37·74]), except for mental disorders (which increased by 32·18% [1·67 to 66·49]), whereas the YLD rate increased slightly (1·44% [0·09 to 2·79]). Positive correlations were observed between DALY rates and SDIs for substance use disorders (rs=0·58, p=0·0012) and skin and subcutaneous diseases (rs=0·45, p=0·017), whereas negative correlations were found between DALY rates and SDIs for cardiovascular diseases (rs=–0·46, p=0·015), neoplasms (rs=–0·57, p=0·0015), and sense organ diseases (rs=–0·61, p=0·0005)

Tight - binding molecural dynamics studies of amorphous and nanostructured carbon networks

The purpose of this dissertation is to study and understand the structural, mechanical and optoelectronic properties of amorphous and nanostructured carbon. To achieve this goal, we carry out molecular dynamics simulations within the tightbinding (or linear combination of atomic orbitals) approximation. Highlights of the work done are the detailed study and analysis of the microstructure, the finding of general physical trends in the variation of basic characteristics, and the development of a methodology for the calculation and analysis of the optical properties. As an introduction to the subject, we first present the elemental properties of carbon, its electronic structure and hybridizations, and the various forms that can be attained by carbon either in the solid state or in nanostructured configurations. Next, we present the theory of the tight-binding method and the two specific models used in this work. We also present the methodology for the computer generation of our networks, as well as the tools used for their analysis. Initially, we study the microstructure of amorphous carbon. We extract the structural parameters of our networks and calculate the distribution functions of bond lengths and bond angles, and perform a statistical analysis of rings. We find that the basic characteristics of the microstructure are in excellent agreement with results from first-principle calculations. After establishing the reliability of our methodology, we study the structural and elastic properties of our amorphous carbon networks. The main finding about the material density is that it has a linear dependence on the sp3 tetrahedral fraction, in good agreement with experimental work and other theoretical calculations. Also, we extract for the first time accurate relations between the bulk modulus and the mean coordination (or equivalently the density) and the mean bond length in the amorphous network. These relations, in a power-law form, are in excellent agreement with mean-field theories for the elastic properties. We continue by investigating the electronic and optical properties of amorphous carbon. Our major contribution here is the development of a methodology to calculate the optical constants from the tight-binding wavefunctions. Initially, we calculate the electronic density of states and the dielectric function, and we then extract the optical gaps and the Urbach energy, associating them with the degree of disorder in our networks. We compare to the literature where it is feasible. Finally, the dissertation is concluded by applying the above well-tested methods to the case of nanostructured carbon.Ο σκοπός της παρούσας διατριβής είναι η μελέτη και κατανόηση των δομικών, μηχανικών και οπτοηλεκτρονικών ιδιοτήτων του αμόρφου και νανοδομικού άνθρακα. Για το σκοπό αυτό χρησιμοποιούμε προσομοιώσεις μοριακής δυναμικής βασισμένες στη μέθοδο της ισχυράς δέσμευσης (ή γραμμικού συνδυασμού ατομικών τροχιακών). Κεντρικά σημεία της διατριβής είναι η λεπτομερής μελέτη της μικροδομής και η εύρεση γενικών τάσεων/σχέσεων για τις μεταβολές των χαρακτηριστικών ιδιοτήτων, καθώς και η ανάπτυξη μιας μεθοδολογίας για τον υπολογισμό των οπτικών ιδιοτήτων. Κατ’ αρχάς, παρουσιάζουμε εισαγωγικά τη φυσική δομή του άνθρακα, τις ιδιότητές του, την ηλεκτρονική διάταξη και τους υβριδισμούς των τροχιακών του, και τις διάφορες μορφές που μπορεί να πάρει ο άνθρακας είτε στη στερεά κατάσταση, ή σε νανοδομικές διαμορφώσεις, πράγμα που είναι απόρροια των παραπάνω. Στη συνέχεια εισάγουμε τη θεωρία της μεθόδου της ισχυράς δέσμευσης και παρουσιάζουμε τα δυο διαφορετικά μοντέλα που θα χρησιμοποιήσουμε. Επίσης συζητάμε τη μεθοδολογία που θα ακολουθήσουμε στην κατασκευή των πλεγμάτων μας, καθώς και τα “εργαλεία” που θα χρειαστούμε για την ανάλυση των ιδιοτήτων του υλικού μας. Αρχικά μελετάμε τη μικροδομή του άμορφου άνθρακα. Εξάγουμε τις δομικές παραμέτρους των πλεγμάτων μας και υπολογίζουμε τις συναρτήσεις κατανομής των μηκών και των γωνιών μεταξύ των δεσμών των ατόμων. Εν συνεχεία κάνουμε μια στατιστική στους δακτυλίους που συναντάμε στο υλικό μας. Βρίσκουμε πως τα βασικά χαρακτηριστικά της μικροδομής είναι σε άριστη συμφωνία με αποτελέσματα από υπολογισμούς πρώτων αρχών. Αφού διαπιστώσουμε την πλήρη αξιοπιστία της μεθοδολογίας, μελετάμε στην επόμενη φάση τις δομικές και τις ελαστικές ιδιότητες των πλεγμάτων μας. Το βασικό συμπέρασμα που προκύπτει για την πυκνότητα των δειγμάτων μας, είναι πως η τελευταία έχει γραμμική εξάρτηση με το ποσοστό των sp3 ατόμων και το αποτέλεσμα αυτό συγκρίνεται με πειραματικά και άλλα θεωρητικά δεδομένα και αποκαλύπτεται συμφωνία μεταξύ 3# τους. Επίσης, εξάγουμε για πρώτη φορά ακριβείς σχέσεις μεταξύ του μέτρου ελαστικότητας όγκου και του μέσου αριθμού συντάξεως (ή της πυκνότητας), και του μέσου μήκους δεσμού στο άμορφο πλέγμα. Οι σχέσεις αυτές, σε μορφή νόμου δυνάμεως, είναι σε εξαιρετική συμφωνία με θεωρίες μέσου πεδίου για τις ελαστικές ιδιότητες. Στη συνέχεια μελετάμε τις ηλεκτρονικές και τις οπτικές ιδιότητες του υλικού μας. Η κύρια συνεισφορά μας εδώ είναι η ανάπτυξη μιας μεθοδολογίας για τον υπολογισμό των οπτικών σταθερών από τις κυματοσυναρτήσεις ισχυράς δέσμευσης. Κατ’αρχάς υπολογίζουμε την ηλεκτρονική πυκνότητα καταστάσεων και τη διηλεκτρική συνάρτηση, και καταλήγουμε στο οπτικό χάσμα και την ενέργεια Urbach και πως αυτά συνδέονται με την αταξία μέσα στα πλέγματα μας. Όλα τα αποτελέσματά μας συγκρίνονται με αντίστοιχα που συναντάμε στη βιβλιογραφία. Τέλος η διατριβή ολοκληρώνεται με την εφαρμογή όλων των παραπάνω στην περίπτωση του νανοδομικού άνθρακα. Αφού πρώτα εδραιώσαμε μια ολοκληρωμένη μεθοδολογία υπολογισμού των ιδιοτήτων του άμορφου άνθρακα, αποφασίσαμε να την ελέγξουμε και στη νανοδομική μορφή του υλικού και εδώ παρουσιάζουμε τα συμπεράσματά μας

Tight-binding molecular dynamics studies of amorphous and nanostructured carbon networks

Ο σκοπός της παρούσας διατριβής είναι η μελέτη και κατανόηση των δομικών,μηχανικών και οπτοηλεκτρονικών ιδιοτήτων του αμόρφου και νανοδομικού άνθρακα. Για το σκοπό αυτό χρησιμοποιούμε προσομοιώσεις μοριακής δυναμικής βασισμένες στη μέθοδο της ισχυράς δέσμευσης (ή γραμμικού συνδυασμού ατομικών τροχιακών). Κεντρικά σημεία της διατριβής είναι η λεπτομερής μελέτη της μικροδομής και η εύρεση γενικών τάσεων/σχέσεων για τις μεταβολές των χαρακτηριστικών ιδιοτήτων, καθώς και η ανάπτυξη μιας μεθοδολογίας για τον υπολογισμό των οπτικών ιδιοτήτων. Κατ’ αρχάς, παρουσιάζουμε εισαγωγικά τη φυσική δομή του άνθρακα, τις ιδιότητές του, την ηλεκτρονική διάταξη και τους υβριδισμούς των τροχιακών του, και τις διάφορες μορφές που μπορεί να πάρει ο άνθρακας είτε στη στερεά κατάσταση, ή σε νανοδομικές διαμορφώσεις, πράγμα που είναι απόρροια των παραπάνω. Στη συνέχεια εισάγουμε τη θεωρία της μεθόδου της ισχυράς δέσμευσης και παρουσιάζουμε τα δυο διαφορετικά μοντέλα που θα χρησιμοποιήσουμε. Επίσης συζητάμε τη μεθοδολογία που θα ακολουθήσουμε στην κατασκευή των πλεγμάτων μας, καθώς και τα “εργαλεία” που θα χρειαστούμε για την ανάλυση των ιδιοτήτων του υλικού μας. Αρχικά μελετάμε τη μικροδομή του άμορφου άνθρακα. Εξάγουμε τις δομικές παραμέτρους των πλεγμάτων μας και υπολογίζουμε τις συναρτήσεις κατανομής των μηκών και των γωνιών μεταξύ των δεσμών των ατόμων. Εν συνεχεία κάνουμε μια στατιστική στους δακτυλίους που συναντάμε στο υλικό μας. Βρίσκουμε πως τα βασικά χαρακτηριστικά της μικροδομής είναι σε άριστη συμφωνία με αποτελέσματα από υπολογισμούς πρώτων αρχών. Αφού διαπιστώσουμε την πλήρη αξιοπιστία της μεθοδολογίας, μελετάμε στην επόμενη φάση τις δομικές και τις ελαστικές ιδιότητες των πλεγμάτων μας. Το βασικό συμπέρασμα που προκύπτει για την πυκνότητα των δειγμάτων μας, είναι πως η τελευταία έχει γραμμική εξάρτηση με το ποσοστό των sp3 ατόμων και το αποτέλεσμα αυτό συγκρίνεται με πειραματικά και άλλα θεωρητικά δεδομένα και αποκαλύπτεται συμφωνία μεταξύ τους. Επίσης, εξάγουμε για πρώτη φορά ακριβείς σχέσεις μεταξύ του μέτρου ελαστικότητας όγκου και του μέσου αριθμού συντάξεως (ή της πυκνότητας), και του μέσου μήκους δεσμού στο άμορφο πλέγμα. Οι σχέσεις αυτές, σε μορφή νόμου δυνάμεως, είναι σε εξαιρετική συμφωνία με θεωρίες μέσου πεδίου για τις ελαστικές ιδιότητες. Στη συνέχεια μελετάμε τις ηλεκτρονικές και τις οπτικές ιδιότητες του υλικού μας. Η κύρια συνεισφορά μας εδώ είναι η ανάπτυξη μιας μεθοδολογίας για τον υπολογισμό των οπτικών σταθερών από τις κυματοσυναρτήσεις ισχυράς δέσμευσης. Κατ’αρχάς υπολογίζουμε την ηλεκτρονική πυκνότητα καταστάσεων και τη διηλεκτρική συνάρτηση, και καταλήγουμε στο οπτικό χάσμα και την ενέργεια Urbach και πως αυτά συνδέονται με την αταξία μέσα στα πλέγματα μας. Όλα τα αποτελέσματά μας συγκρίνονται με αντίστοιχα που συναντάμε στη βιβλιογραφία. Τέλος η διατριβή ολοκληρώνεται με την εφαρμογή όλων των παραπάνω στην περίπτωση του νανοδομικού άνθρακα. Αφού πρώτα εδραιώσαμε μια ολοκληρωμένη μεθοδολογία υπολογισμού των ιδιοτήτων του άμορφου άνθρακα, αποφασίσαμε να την ελέγξουμε και στη νανοδομική μορφή του υλικού και εδώ παρουσιάζουμε τα συμπεράσματά μας.The purpose of this dissertation is to study and understand the structural, mechanical and optoelectronic properties of amorphous and nanostructured carbon. To achieve this goal, we carry out molecular dynamics simulations within the tightbinding (or linear combination of atomic orbitals) approximation. Highlights of the work done are the detailed study and analysis of the microstructure, the finding of general physical trends in the variation of basic characteristics, and the development of a methodology for the calculation and analysis of the optical properties. As an introduction to the subject, we first present the elemental properties of carbon, its electronic structure and hybridizations, and the various forms that can be attained by carbon either in the solid state or in nanostructured configurations. Next, we present the theory of the tight-binding method and the two specific models used in this work. We also present the methodology for the computer generation of our networks, as well as the tools used for their analysis. Initially, we study the microstructure of amorphous carbon. We extract the structural parameters of our networks and calculate the distribution functions of bond lengths and bond angles, and perform a statistical analysis of rings. We find that the basic characteristics of the microstructure are in excellent agreement with results from first-principle calculations. After establishing the reliability of our methodology, we study the structural and elastic properties of our amorphous carbon networks. The main finding about the material density is that it has a linear dependence on the sp3 tetrahedral fraction, in good agreement with experimental work and other theoretical calculations. Also, we extract for the first time accurate relations between the bulk modulus and the mean coordination (or equivalently the density) and the mean bond length in the amorphous network. These relations, in a power-law form, are in excellent agreement with mean-field theories for the elastic properties. We continue by investigating the electronic and optical properties of amorphous carbon. Our major contribution here is the development of a methodology to calculate the optical constants from the tight-binding wavefunctions. Initially, we calculate the electronic density of states and the dielectric function, and we then extract the optical gaps and the Urbach energy, associating them with the degree of disorder in our networks. We compare to the literature where it is feasible. Finally, the dissertation is concluded by applying the above well-tested methods to the case of nanostructured carbon

Computer Simulations of Nanostructured Carbon Under Tensile Load: Electronic Structure and Optical Gap

We use computer simulations to study the behavior of amorphous carbon and carbon composites under tensile strain. We investigate the behavior of the optoelectronic properties of these materials as strain is increased. These properties are monitored through the electronic density of states, the optical gap and the Urbach energy for both materials. The variation in the hybrid (sp 2 and sp 3) content due to the external load is directly connected to changes in the optoelectronic properties with increasing strain. This connection will lead to interesting features in the Urbach edge for the amorphous network, while the respective effect for the nanocomposite will be less pronounced. The situation is reversed when the optical gap is used as a probe of the properties of both amorphous and composite materials

Modelling of Three-Dimensional Nanographene

Monte Carlo simulations and tight-binding calculations shed light on the properties of three-dimensional nanographene, a material composed of interlinked, covalently-bonded nanoplatelet graphene units. By constructing realistic model networks of nanographene, we study its structure, mechanical stability, and optoelectronic properties. We find that the material is nanoporous with high specific surface area, in agreement with experimental reports. Its structure is characterized by randomly oriented and curved nanoplatelet units which retain a high degree of graphene order. The material exhibits good mechanical stability with a formation energy of only ∼0.3 eV/atom compared to two-dimensional graphene. It has high electrical conductivity and optical absorption, with values approaching those of graphene

Atomistic simulations of low-density nanoporous materials: Carbon nanofoams

Atomistic simulations give new insights into the properties of carbon nanofoams, a low-density nanoporous and nanostructured material. It is shown that agglomeration, crosslinking, and deformation, processes that are often ignored in theoretical descriptions of nanomaterials, have a dramatic effect on their properties. A most striking finding is that nanofoams composed exclusively of semiconducting nanostructures turn out to be metallic with high conductivity and optical absorptance. The underlying mechanism may explain relevant observations in other nanoporous materials. The simulated structures contain trivalent carbon atoms, suggested earlier to be a major source of magnetism in these materials