Transparent conducting materials(TCMs)have been widely used in optoelectronic applications such as touchscreens,flat panel displays and thin film solar cells.These applications of TCMs are currently dominated by n-typ...Transparent conducting materials(TCMs)have been widely used in optoelectronic applications such as touchscreens,flat panel displays and thin film solar cells.These applications of TCMs are currently dominated by n-type doped oxides.High-performance p-type TCMs are still lacking due to their low hole mobility or p-type doping bottleneck,which impedes efficient device design and novel applications such as transparent electronics.Here,based on first-principles calculations,we propose chalcogenide perovskite YScS3 as a promising p-type TCM.According to our calculations,its optical absorption onset is above 3 eV,which allows transparency to visible light.Its hole conductivity effective mass is 0.48 m0,which is among the smallest in p-type TCMs,suggesting enhanced hole mobility.It could be doped to p-type by group-Ⅱelements on cation sites,all of which yield shallow acceptors.Combining these properties,YSCS3 holds great promise to enhancing the performance of p-type TCMs toward their n-type counterparts.展开更多
We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10...We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10 method for density functional theory calculations.Our benchmark is based on two molecules:glycine(or Gly,an amino acid)and uracil(or U,an RNA base).We consider six dimer configurations of the two monomers and their potential energy surfaces as a function of relative distance and rotation angle.The Gly-Gly,Gly-U,and U-U pairs represent London dispersion,hydrogen bonding,andπ–πstacking interactions,respectively.Our results show that both PBE+D3 and SCAN+rVV10 methods can yield accuracy better than 1 kcal/mol,except for the cases when the distance between the two monomers is significantly smaller than the equilibrium distance.In such a case,neither of these methods can yield uniformly accurate results for all the configurations.In addition,it is found that the SCAN and SCAN+rVV10 methods can reproduce some subtle features in a rotational potential energy curve,while the PBE,PBE+D3,and the local density approximation fail.展开更多
The physics of flat band is novel and rich but difficult to access.In this regard,recently twisting of bilayer van der Waals(vd W)-bounded two-dimensional(2 D)materials has attracted much attention,because the reducti...The physics of flat band is novel and rich but difficult to access.In this regard,recently twisting of bilayer van der Waals(vd W)-bounded two-dimensional(2 D)materials has attracted much attention,because the reduction of Brillouin zone will eventually lead to a diminishing kinetic energy.Alternatively,one may start with a 2 D kagome lattice,which already possesses flat bands at the Fermi level,but unfortunately these bands connect quadratically to other(dispersive)bands,leading to undesirable effects.Here,we propose,by first-principles calculation and tight-binding modeling,that the same bilayer twisting approach can be used to isolate the kagome flat bands.As the starting kinetic energy is already vanishingly small,the interlayer vd W potential is always sufficiently large irrespective of the twisting angle.As such the electronic states in the(connected)flat bands become unstable against a spontaneous Wigner crystallization,which is expected to have interesting interplays with other flat-band phenomena such as novel superconductivity and anomalous quantum Hall effect.展开更多
High-temperature phases of solids are often dynamically stable only.First-principles study of point defects in such solids at 0 K is prohibited by their static instability,which results in random structures of the def...High-temperature phases of solids are often dynamically stable only.First-principles study of point defects in such solids at 0 K is prohibited by their static instability,which results in random structures of the defect-containing supercell so that the total energy of the supercell is randomly affected by structural distortions far away from the defect.Taking cubic perovskiteα-Cs Pb I_(3) as an example,we first present the problem incurred by the static instability and then propose an approach based on molecular dynamics to carry out ensemble average for tackling the problem.Within affordable simulation time,we obtain converged defect ionization energies,which are unattainable by a standard approach and allow us to evaluate its defect tolerance property.Our work paves the way for studying defects in statically unstable solids.展开更多
Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applicati...Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.展开更多
Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensivel...Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensively,the photochromic mechanism in YH_xO_yremains unknown Here,using excited-state molecular dynamics simulation based on the recently developed real-time time-dependent density functional theory(RT-TDDFT)method,we study the photochemical reactions in YH_xO_y.We find that under photoexcitation,dihydrogen defects are formed within 100 fs.The dihydrogen defect behaves as a shallow donor and renders the material strongly n-type doped,which could be responsible for the photochromic effect observed in YH_xO_y.We also find that oxygen concentration affects the metastability of the dihydrogen species,meaning that the energy barrier for the dihydrogen to dissociate is related to the oxygen concentration The highest barrier of 0.28 eV is found in our model with O/Y=1:8.If the oxygen concentration is too low,the dihydrogen will quickly dissociate when the excitation is turned off.If the oxygen concentration is too high,the dihydrogen dissociates even when the excitation is still on.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11774365)supported by the Natural Science Foundation of Shanghai+3 种基金China(Grant No.19ZR1421800)the Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures(Grant No.SKL 201804)supported by the U.S.NSF(Grant Nos.CBET-1510121 and CBET-1510948)supported by the U.S.DOE(Grant No.DE-SC0002623)。
文摘Transparent conducting materials(TCMs)have been widely used in optoelectronic applications such as touchscreens,flat panel displays and thin film solar cells.These applications of TCMs are currently dominated by n-type doped oxides.High-performance p-type TCMs are still lacking due to their low hole mobility or p-type doping bottleneck,which impedes efficient device design and novel applications such as transparent electronics.Here,based on first-principles calculations,we propose chalcogenide perovskite YScS3 as a promising p-type TCM.According to our calculations,its optical absorption onset is above 3 eV,which allows transparency to visible light.Its hole conductivity effective mass is 0.48 m0,which is among the smallest in p-type TCMs,suggesting enhanced hole mobility.It could be doped to p-type by group-Ⅱelements on cation sites,all of which yield shallow acceptors.Combining these properties,YSCS3 holds great promise to enhancing the performance of p-type TCMs toward their n-type counterparts.
基金supported by US National Science Foundation under Grant No. DMREF-1627028
文摘We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10 method for density functional theory calculations.Our benchmark is based on two molecules:glycine(or Gly,an amino acid)and uracil(or U,an RNA base).We consider six dimer configurations of the two monomers and their potential energy surfaces as a function of relative distance and rotation angle.The Gly-Gly,Gly-U,and U-U pairs represent London dispersion,hydrogen bonding,andπ–πstacking interactions,respectively.Our results show that both PBE+D3 and SCAN+rVV10 methods can yield accuracy better than 1 kcal/mol,except for the cases when the distance between the two monomers is significantly smaller than the equilibrium distance.In such a case,neither of these methods can yield uniformly accurate results for all the configurations.In addition,it is found that the SCAN and SCAN+rVV10 methods can reproduce some subtle features in a rotational potential energy curve,while the PBE,PBE+D3,and the local density approximation fail.
基金the National Natural Science Foundation of China(Grant No.11874314)supported by U.S.DOE under Grant No.DE-SC0002623。
文摘The physics of flat band is novel and rich but difficult to access.In this regard,recently twisting of bilayer van der Waals(vd W)-bounded two-dimensional(2 D)materials has attracted much attention,because the reduction of Brillouin zone will eventually lead to a diminishing kinetic energy.Alternatively,one may start with a 2 D kagome lattice,which already possesses flat bands at the Fermi level,but unfortunately these bands connect quadratically to other(dispersive)bands,leading to undesirable effects.Here,we propose,by first-principles calculation and tight-binding modeling,that the same bilayer twisting approach can be used to isolate the kagome flat bands.As the starting kinetic energy is already vanishingly small,the interlayer vd W potential is always sufficiently large irrespective of the twisting angle.As such the electronic states in the(connected)flat bands become unstable against a spontaneous Wigner crystallization,which is expected to have interesting interplays with other flat-band phenomena such as novel superconductivity and anomalous quantum Hall effect.
基金supports from Shanghai International Cooperation Project(Grant No.20520760900)the Major Science and Technology Programs of Yunnan(Grant No.202002AB080001-1)+2 种基金supports from the Natural Science Foundation of Shanghai(Grant No.19ZR1421800)supports from the US National Science Foundation(Grant No.CBET-1510948)Part of the calculations was conducted at Stampede supercomputer resources at TACC made available by Extreme Science and Engineering Discovery Environment(XSEDE)through Allocation(Grant No.TG-DMR180114),which was supported by US National Science Foundation(Grant No.ACI-1548562)。
文摘High-temperature phases of solids are often dynamically stable only.First-principles study of point defects in such solids at 0 K is prohibited by their static instability,which results in random structures of the defect-containing supercell so that the total energy of the supercell is randomly affected by structural distortions far away from the defect.Taking cubic perovskiteα-Cs Pb I_(3) as an example,we first present the problem incurred by the static instability and then propose an approach based on molecular dynamics to carry out ensemble average for tackling the problem.Within affordable simulation time,we obtain converged defect ionization energies,which are unattainable by a standard approach and allow us to evaluate its defect tolerance property.Our work paves the way for studying defects in statically unstable solids.
基金supported by the National Natural Science Foundation of China (11774365)the Natural Science Foundation of Shanghai (19ZR1421800)+4 种基金Shanghai International Cooperation Project (20520760900)the Opening Project and Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures (SKL201804 and SKL201803SIC) support by US National Science Foundation (NSF) (CBET1510121)US Department of Energy (DOE) (DEEE0007364)support by US NSF (CBET-1510948).support by US NSF (DMR-1506669)support by the Fundamental Research Funds for the Central Universities (DUT21RC(3) 033)。
文摘Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.
基金the support by the National Natural Science Foundation of China(11774365)。
文摘Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensively,the photochromic mechanism in YH_xO_yremains unknown Here,using excited-state molecular dynamics simulation based on the recently developed real-time time-dependent density functional theory(RT-TDDFT)method,we study the photochemical reactions in YH_xO_y.We find that under photoexcitation,dihydrogen defects are formed within 100 fs.The dihydrogen defect behaves as a shallow donor and renders the material strongly n-type doped,which could be responsible for the photochromic effect observed in YH_xO_y.We also find that oxygen concentration affects the metastability of the dihydrogen species,meaning that the energy barrier for the dihydrogen to dissociate is related to the oxygen concentration The highest barrier of 0.28 eV is found in our model with O/Y=1:8.If the oxygen concentration is too low,the dihydrogen will quickly dissociate when the excitation is turned off.If the oxygen concentration is too high,the dihydrogen dissociates even when the excitation is still on.
