First-Principles Calculations of Energy Materials

Department of ChemistrySince the advent of civilization, carbon-based fuel, which harvests energy by oxidizing carbon, has been the main strategy for energy conversion. However, the harmful byproducts of the carbon oxidation reaction such as NO$_x$ and CO$_2$ gas are inevitable and are becoming a serious problem threatening the ordinary life of the human being. Thus, low-cost, efficient, and eco-friendly energy conversion is one of the key future technologies for sustainable development. In this thesis, we discuss the first-principles calculations of energy conversion materials, including lead halide perovskite(LHP) solar cell, heterogeneous single atom catalysts (SAC), and graphene/Cu single photon source using the density functional theory(DFT), wave-function theory(WFT), and many-body theory. Also we derive the solution of the nonequilibrium steady state Anderson impurity model in real frequency using the pseudo-particle (slave-boson) method by including vertex terms beyond the first-order approximation. Solar energy that converts the photon energy into the electric current has been considered as the alternative energy harvesting to carbon fuel. In the past five years, lead halide perovskite ABX$_3$ (A=Cs$^+$, CH$_3$NH$_3^+$(MA), CHN$_2$H$_4^+$(FA), N$_2$H$_5^+$(HZ); B=Pb$^{2+}$; X=Cl$^-$, Br$^-$ or I$^-$) solar cells(PSCs) has shown great success with the power conversion efficiency(PCE) of 23.7 \% rapidly reaching the Shockley???Queisser limit ($\sim 30 \%$). The recent discovery of long life-time of hot-electrons may even enable LHP solar cells to overcome the Shockley???Queisser limit. Also LHPs in low dimensions ($\le 2$) can be utilized as the light emitting diodes(LED) with the wide range of wavelengths. Recent experiments have achieved the high luminescence efficiency on a par with organic LED making LHPs promising as a versatile energy material. We uncover four intriguing results of theoretical calculations of LHPs: (i) Polaronic nature of lead halide PSCs and the role of A-site cation for polaron tuning, (ii) Rashba-Dresselhaus spin-orbit effect at LHP interface with electron transport layers, (iii) Conduction band alignment mechanism of MAPbI$_3$/La-doped BaSnO$_3$(LBSO) interface, and (iv) Proton-mediated band alignment mechanism in TiO$_2$/MAPbI$_3$. Generally, the electrons in crystals experience a degree of deformation of a surrounding lattice in addition to the Bloch potential because of the large polarity of the ionic crystal giving rise to polaron. There has been a critical debate on the main source of electron-phonon coupling(e-ph) being either optical or acoustic phonon in LHPs. We show that the source of e-ph coupling in LHPs is the highest LO phonon and investigate the correlation between the polaron and A-site cations. We show that the coordination of A-site cation to halides is important to determine the polaron mobility of LHPs. The spin-orbit coupling(SOC) field, which is odd function in $k$(momentum) and time reversal symmetric, at the interface of hetero-structures gives rise to the Rashba-Dresselhaus(RD) splitting of the degenerate bands. We study an elusive part of LHP/graphene and LHP/ETL interfaces using DFT and {\it ab initio} molecular dynamics(AIMD) simulations to account for RD spin-orbit effect. We carry out the calculations for graphene/cubic-CsPbI$_3$(001) as a prospective interface for improving carrier transport and for TiO$_2$/cubic-MAPbI$_3$(001) which is a well-known ETL material for PSC devices. Anatase and rutile TiO$_2$ has been the most widely used electron transport layer (ETL) material in lead halide PSC devices. However, the photo-degradation of TiO$_2$ by ultraviolet (UV) rays gradually deteriorates the device performance. To overcome this obstacle, the development of efficient and reliable next-generation ETL substances has emerged recently. Metal oxide materials such as SnO$_2$, ZnO, WO$_3$, ZnSnO$_4$ are drawing attention as the next-generation ETL. Thus, using DFT at the PBE0+spin???orbit coupling(SOC)+Grimme-D3 van der Waals level of theory, we study a recently discovered La-doped BaSnO$_3$, which has achieved 22 $\%$ PCE, and discuss the key factor for the optimal band alignment at the MAPbI$_3$/LBSO interface. Organic cations such as MA in LHPs have the rotational degrees of freedom. However, we show that the rotational degrees of freedom of MA's dipole at the TiO$_2$/perovskite interface is significantly suppressed. We study the interface between rutile TiO$_2$ and cubic MAPbI$_3$ using DFT and AIMD simulations and show that proton-mediated electron transfer process exists because of the strong short hydrogen bonding, which is a drastically different picture compared to the bulk. The developments of hydrogen-based energy conversion and storage are imperative for the efficient and environment-friendly future energy fuel. A theoretical understanding of the water splitting reaction (hydrogen evolution reaction(HER) at the cathode and oxygen evolution reaction(OER) at the anode) is therefore crucial for the design of artificial HER/OER catalysts. From the HER experiment of Pt-Graphitic tube-FeCo/Cu system, we provide a mechanism for the superb HER which showed extremely high turnover frequency(7.2/s), low overpotential(18 meV at 10 mA/cm$^2$), and small Tafel slope(24 mV$\cdot$dec$^{-1}$) using ultra-low Pt loading. Though single Pt-C$_2$N$_2$ in graphitic tube has ideal free energy ($\Delta$G $\approx$ 0) for HER, the conductivity is very low limiting the steady state mass transfer of electrons inside the cathode. We show that Pt single atoms in the presence of Pt clusters drastically improves the conductivity of the graphitic tubes and hence the activity of the Pt single atoms. We also study the core-level X-ray absorption spectrum of single atom catalyst systems using \textit{ab initio} methods. Nonequilibrium quantum mechanics is still a challenging area awaiting for a general theory like the imaginary-time method of equilibrium quantum mechanics. In a steady state, we need a general framework of nonequilibrium quantum mechanics instead of the real-time propagation which is system-dependent and is limited to high-energy regime(or ultra-fast process $\sim fs$). We derive an analytic solution of the nonequilibrium Anderson impurity model on Keldysh contour(steady state) by including vertex corrections(called one-crossing approximation) in frequency domain using pseudo-particle formalism. We derive the lesser(greater) pseudo-particle self-energy(empty, singly-occupied, doubly-occupied) and the lesser(greater) impurity Green's function to obtain the impurity spectral function and the DC current through the impurity. We can access to a low energy scale which had been formidable to the real-time propagation methods. The nonequilibrium solution exactly corresponds to the equilibrium solution at the equilibrium limit.clos

Going for Gold(-Standard): Attaining Coupled Cluster Accuracy in Oxide-Supported Nanoclusters

Metal nanoclusters supported on oxide surfaces are widely-used catalysts that boasts sharply enhanced activity over their bulk, especially for the coinage metals: Au, Ag and Cu. These properties depend sensitively on the nanocluster structure, which are challenging to model with density functional theory (DFT) -- the workhorse modelling technique. Leveraging the recently developed SKZCAM protocol, we perform the first ever benchmark study of coinage metal structures on the MgO surface with coupled cluster theory [CCSD(T)] -- the gold-standard modelling technique. We investigate a comprehensive range of DFT models (exchange-correlation functional and dispersion correction) and our benchmarks reveal that none of the investigated models can accurately describe this system. We demonstrate that this arises from inadequate account of metal-metal interactions in the nanocluster and propose a high-level correction which provides reference accuracy at low cost. This forges a path towards studying larger systems, which we highlight by benchmarking Au$_{20}$ on MgO, a challenging system where DFT models have disagreed on its ground state structure.Comment: Working pape

A Bayesian Committee Machine Potential for Organic Nitrogen Compounds

Large-scale computer simulations of chemical atoms are used in a wide range of applications, including batteries, drugs, and more. However, there is a problem with efficiency as it takes a long time due to the large amount of calculation. To solve these problems, machine learning interatomic potential (ML-IAP) technology is attracting attention as an alternative. ML-IAP not only has high accuracy by faithfully expressing the density functional theory (DFT), but also has the advantage of low computational cost. However, there is a problem that the potential energy changes significantly depending on the environment of each atom, and expansion to a wide range of compounds within a single model is still difficult to build in the case of a kernel-based model. To solve this problem, we would like to develop a universal ML-IAP using this active Bayesian Committee Machine (BCM) potential methodology for carbon-nitrogen-hydrogen (CNH) with various compositions. ML models are trained and generated through first-principles calculations and molecular dynamics simulations for molecules with only CNH. Using long amine structures to test an ML model trained only with short chains, the results show excellent consistency with DFT calculations. Consequently, machine learning-based models for organic molecules not only demonstrate the ability to accurately describe various physical properties but also hold promise for investigating a broad spectrum of diverse materials systems

Efficient electron extraction of SnO(2)electron transport layer for lead halide perovskite solar cell

SnO(2)electron transport layer (ETL) has been spotlighted with its excellent electron extraction and stability over TiO2ETL for perovskite solar cells (PSCs), rapidly approaching the highest power conversion efficiency. Thus, how to boost the performance of ETL is of utmost importance and of urgent need in developing more efficient PSCs. Here we elucidate the atomistic origin of efficient electron extraction and long stability of SnO2-based PSCs through the analysis of band alignment, carrier injection, and interfacial defects in the SnO2/MAPbI(3)(MA = CH3NH3+) interface using unprecedentedly high level of first-principles calculations at the PBE0 + spin-orbit-coupling + dispersion-correction level for all possible terminations and MA directions. We find that Sn-sorbital plays a crucial role in carrier injection and defect tolerance. SnO2/MAPbI(3)shows favorable conduction band alignments at both MAI- and PbI2-terminations, which makes the solar cell performance of SnO2/MAPbI(3)excel that of TiO2/MAPbI(3). Different electron transfer mechanisms of dipole interaction and orbital hybridization at the MAI- and PbI2-terminations indicate that post-transition metal (spvalence) oxide ETLs would outperform transition metal (dvalence) oxide ETLs for PSCs

Stimulation-Induced Side Effects of Deep Brain Stimulation in the Ventralis Intermedius and Posterior Subthalamic Area for Essential Tremor

Deep brain stimulation (DBS) targeting the ventralis intermedius (VIM) nucleus of the thalamus and the posterior subthalamic area (PSA) has been shown to be an effective treatment for essential tremor (ET). The aim of this study was to compare the stimulation-induced side effects of DBS targeting the VIM and PSA using a single electrode. Patients with medication-refractory ET who underwent DBS electrode implantation between July 2011 and October 2020 using a surgical technique that simultaneously targets the VIM and PSA with a single electrode were enrolled in this study. A total of 93 patients with ET who had 115 implanted DBS electrodes (71 unilateral and 22 bilateral) were enrolled. The Clinical Rating Scale for Tremor (CRST) subscores improved from 20.0 preoperatively to 4.3 (78.5% reduction) at 6 months, 6.3 (68.5% reduction) at 1 year, and 6.5 (67.5% reduction) at 2 years postoperation. The best clinical effect was achieved in the PSA at significantly lower stimulation amplitudes. Gait disturbance and clumsiness in the leg was found in 13 patients (14.0%) upon stimulation of the PSA and in significantly few patients upon stimulation of the VIM (p = 0.0002). Fourteen patients (15.1%) experienced dysarthria when the VIM was stimulated; this number was significantly more than that with PSA stimulation (p = 0.0233). Transient paresthesia occurred in 13 patients (14.0%) after PSA stimulation and in six patients (6.5%) after VIM stimulation. Gait disturbance and dysarthria were significantly more prevalent in patients undergoing bilateral DBS than in those undergoing unilateral DBS (p = 0.00112 and p = 0.0011, respectively). Paresthesia resolved either after reducing the amplitude or switching to bipolar stimulation. However, to control gait disturbance and dysarthria, some loss of optimal tremor control was necessary at that particular electrode contact. In the present study, the most common stimulation-induced side effect associated with VIM DBS was dysarthria, while that associated with PSA DBS was gait disturbance. Significantly, more side effects were associated with bilateral DBS than with unilateral DBS. Therefore, changing active DBS contacts to simultaneous targeting of the VIM and PSA may be especially helpful for ameliorating stimulation-induced side effects

Pharmacologic Activation of Angiotensin-Converting Enzyme II Alleviates Diabetic Cardiomyopathy in db/db Mice by Reducing Reactive Oxidative Stress

Background Diabetes mellitus is one of the most common chronic diseases worldwide, and cardiovascular disease is the leading cause of morbidity and mortality in diabetic patients. Diabetic cardiomyopathy (DCM) is a phenomenon characterized by a deterioration in cardiac function and structure, independent of vascular complications. Among many possible causes, the renin-angiotensin-aldosterone system and angiotensin II have been proposed as major drivers of DCM development. In the current study, we aimed to investigate the effects of pharmacological activation of angiotensin-converting enzyme 2 (ACE2) on DCM. Methods The ACE2 activator diminazene aceturate (DIZE) was administered intraperitoneally to male db/db mice (8 weeks old) for 8 weeks. Transthoracic echocardiography was used to assess cardiac mass and function in mice. Cardiac structure and fibrotic changes were examined using histology and immunohistochemistry. Gene and protein expression levels were examined using quantitative reverse transcription polymerase chain reaction and Western blotting, respectively. Additionally, RNA sequencing was performed to investigate the underlying mechanisms of the effects of DIZE and identify novel potential therapeutic targets for DCM. Results Echocardiography revealed that in DCM, the administration of DIZE significantly improved cardiac function as well as reduced cardiac hypertrophy and fibrosis. Transcriptome analysis revealed that DIZE treatment suppresses oxidative stress and several pathways related to cardiac hypertrophy. Conclusion DIZE prevented the diabetes mellitus-mediated structural and functional deterioration of mouse hearts. Our findings suggest that the pharmacological activation of ACE2 could be a novel treatment strategy for DCM

Association between atherogenic dyslipidemia and muscle quality defined by myosteatosis

BackgroundMyosteatosis, ectopic fat accumulation in skeletal muscle, is a crucial component of sarcopenia, linked to various cardiometabolic diseases. This study aimed to analyze the association between dyslipidemia and myosteatosis using abdominal computed tomography (CT) in a large population.MethodsThis study included 11,823 patients not taking lipid-lowering medications with abdominal CT taken between 2012 and 2013. Total abdominal muscle area (TAMA), measured at the L3 level, was segmented into skeletal muscle area (SMA) and intramuscular adipose tissue. SMA was further classified into normal attenuation muscle area (NAMA: good quality muscle) and low attenuation muscle area (poor quality muscle). NAMA divided by TAMA (NAMA/TAMA) represents good quality muscle. Atherosclerotic dyslipidemia was defined as high-density lipoprotein cholesterol (HDL-C) less than 40 mg/dL in men and 50 mg/dL in women, low-density lipoprotein cholesterol (LDL-C) greater than 160 mg/dL, triglycerides (TG) greater than 150 mg/dL, small dense LDL-C (sdLDL-C) greater than 50.0 mg/dL, or apolipoprotein B/A1 (apoB/A1) greater than 0.08.ResultsThe adjusted odds ratios (ORs) of dyslipidemia according to the HDL-C and sdLDL definitions were greater in both sexes in the lower quartiles (Q1~3) of NAMA/TAMA compared with Q4. As per other definitions, the ORs were significantly increased in only women for LDL-C and only men for TG and ApoB/A1. In men, all lipid parameters were significantly associated with NAMA/TAMA, while TG and ApoB/A1 did not show significant association in women.ConclusionMyosteatosis measured in abdominal CT was significantly associated with a higher risk of dyslipidemia. Myosteatosis may be an important risk factor for dyslipidemia and ensuing cardiometabolic diseases

大韓獸醫學會誌 (2015) 第 55 卷 第 1 號

Abstract : A 14-year-old, 7.4 kg, neutered male mongrel dog presented with vomiting, anorexia, and hematuria starting 3 days prior to admission. Serum biochemical profiles indicated severe azotemia. Computed tomography revealed loss of normal left kidney structure. The organ was 1.5 to 2 times larger than the right kidney with mixed attenuation. Histopathologic examination was performed after nephrectomy. The renal mass and mesenteric membrane were positive for vimentin and stained blue with Masson's trichrome. In conclusion, this was a rare occurrence of primary renal fibrosarcoma, most likely originated from the renal capsule, with local invasion into the mesenteric membrane