Absence of Spin Liquid Phase in the J1−J2J_1-J_2 Heisenberg model on the Square Lattice

We perform an in-depth investigation of the phase diagram of the $J_1-J_2$ Heisenberg model on the square lattice. We take advantage of Density Matrix Renormalization Group and Fully-Augmented Matrix Product States methods and reach unprecedented accuracy with large bond dimensions. We utilize excited-level crossing analysis to pinpoint the phase transition points. It was believed before that there exists a narrow spin liquid phase sandwiched by the N\'eel antiferromagnetic (AFM) and valence bond solid (VBS) phases. Through careful finite size scaling of the level crossing points, we find a direct phase transition between the N\'eel AFM and VBS phases at $J_2/J_1 = 0.535(3)$, suggesting the absence of an intermediate spin liquid phase. We also provide accurate results for ground state energies for a variety of sizes, from which we find the transition between the N\'eel AFM and VBS phases is continuous. These results indicate the existence of a deconfined quantum critical point at $J_2/J_1 = 0.535(3)$ in the model. From the crossing of the first derivative of the energies with $J_2$ for different sizes, we also determine the precise location of the first order phase transition between the VBS and stripe AFM phases at $J_2/J_1=0.610(5)$.Comment: 4 pages, 4 figures, with supplementary material

On the Magnetization of the 120∘120^\circ order of the Spin-1/2 Triangular Lattice Heisenberg Model: a DMRG revisit

We revisit the issue about the magnetization of the $120^\circ$ order in the spin-1/2 triangular lattice Heisenberg model (TLHM) with Density Matrix Renormalization Group (DMRG). The accurate determination of the magnetization of this model is challenging for numerical methods and its value exhibits substantial disparities across various methods. We perform a large-scale DMRG calculation of this model by employing bond dimension as large as $D = 24000$ and by studying the system with width as large as $L_\mathrm{y} = 12$. With careful extrapolation with truncation error and suitable finite size scaling, we give a conservative estimation of the magnetization as $M_0 = 0.208(8)$. The ground state energy per site we obtain is $E_g = -0.5503(8)$. Our results provide valuable benchmark values for the development of new methods in the future.Comment: 6 pages, 6 figure

Exchanging the order of carotenogenic genes linked by porcine teschovirus-1 2A peptide enable to optimize carotenoid metabolic pathway in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae serves as a promising host for the production of a wide range of chemical compounds and fuels. Currently, simultaneous expression of several genes could be achieved via the use of 2A viral peptides, yet detailed characterizations to assess the discrepancy of different orders of genes linked by 2A peptides are rarely sufficient. In this study, we investigated the effects of the order of genes linked by porcine teschovirus-1 2A (P2A) peptide on the metabolic pathway in S. cerevisiae. A heterologous carotenoid biosynthetic system involving nine kinds of polycistronic expression of codon-optimized carotenogenic genes GGPPS, CARB and CARRP from Blakeslea trispora was introduced into S. cerevisiae. The order of genes in the polycistronic segment was exchanged; -carotene production by engineered yeasts was significantly different. The highest -carotene yield was achieved in transformants carrying the plasmid, with CARB as the first gene in the polycistronic construct regardless of the location of GGPPS, CARRP. In addition, we found that -carotene production was coupled with the growth in engineered strain with the highest -carotene content during the shake flask fermentation and fed-batch fermentation. A novel microbial heterologous carotenoid production system was established by optimizing the order of genes linked by P2A peptide sequences in a polycistronic expression construct. The observation of the importance of the order in a polycistronic construct may be used to increase yields in other P2A peptide-containing expression systems

Dithienosilole-Based Small-Molecule Organic Solar Cells with an Efficiency over 8%: Investigation of the Relationship between the Molecular Structure and Photovoltaic Performance

Two new acceptor–donor–acceptor (A-D-A) small molecules with 2,6-(4,4-bis­(2-ethylhexyl)-4H-cyclopenta­[2,1-b;3,4-b′]-dithiophene (DTC) and (4,4′-bis­(2-ethylhexyl) dithieno­[3,2-b:2′,3′-d]­silole)–2,6-diyl (DTS) as the central building block unit and 3-ethyl-rhodanine as the end-capping groups have been designed and synthesized. The influence of the bridging atoms on the optical, electrochemical properties, packing properties, morphology, and device performance of these two molecules was systematically investigated. Although with only the difference of one atom on the central core units, the two molecules showed great different properties such as film absorption, molecular packing, and charge transport properties. The optimized device based on molecule DR3TDTS exhibited a power conversion efficiency (PCE) of >8%

Solution-Processed Organic Solar Cells Based on Dialkylthiol-Substituted Benzodithiophene Unit with Efficiency near 10%

A small molecule named DR3TSBDT with dialkylthiol-substituted benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithio­phene (BDT) as the central unit was designed and synthesized for solution-processed bulk-heterojunction solar cells. A notable power conversion efficiency of 9.95% (certified 9.938%) has been achieved under AM 1.5G irradiation (100 mW cm^–2), with an average PCE of 9.60% based on 50 devices

Small Molecules Based on Alkyl/Alkylthio-thieno[3,2‑<i>b</i>]thiophene-Substituted Benzo[1,2‑<i>b</i>:4,5-b′]dithiophene for Solution-Processed Solar Cells with High Performance

Two acceptor–donor–acceptor small molecules based on thieno­[3,2-<i>b</i>]­thiophene-substituted benzo­[1,2-b:4,5-<i>b</i>′]­dithiophene, DRBDT-TT with alkyl side chain and DRBDT-STT with alkylthio side chain, were designed and synthesized. Both molecules exhibit good thermal stability, suitable energy levels, and ordered molecular packing. Replacing the alkyl chain with alkylthio increases the dihedral angle between the thieno­[3,2-<i>b</i>]­thiophene (TT) and benzo­[1,2-b:4,5-<i>b</i>′]­dithiophene (BDT) unit, and thus slightly decreases its intermolecular interactions leading to its blue-shift absorption in the solid state. The best devices based on DRBDT-TT and DRBDT-STT both exhibited power conversion efficiencies (PCEs) over 8% with high fill factors (FFs) over 0.70 under AM 1.5G irradiation (100 mW cm^–2), which are attributed to their optimized morphologies with feature size of 20–30 nm and well-balanced charge transport properties. The devices based on DRBDT-STT exhibited relatively lower short-circuit current density (<i>J</i>_sc) and thus slightly lower PCE as compared to the devices of DRBDT-TT, mainly due to its relatively poorer absorption. These results demonstrate that thieno­[3,2-<i>b</i>]­thiophene-substituted benzo­[1,2-b:4,5-<i>b</i>′]­dithiophene derivatives could be promising donor materials for obtaining high efficiencies and fill factors

Solution-Processed and High-Performance Organic Solar Cells Using Small Molecules with a Benzodithiophene Unit

Three small molecules named DR3TBDTT, DR3TBDTT-HD, and DR3TBD2T with a benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene (BDT) unit as the central building block have been designed and synthesized for solution-processed bulk-heterojunction solar cells. Power conversion efficiencies (PCEs) of 8.12% (certified 7.61%) and 8.02% under AM 1.5G irradiation (100 mW cm^–2) have been achieved for DR3TBDTT- and DR3TBDT2T-based organic photovoltaic devices (OPVs) with PC₇₁BM as the acceptor, respectively. The better PCEs were achieved by improving the short-circuit current density without sacrificing the high open-circuit voltage and fill factor through the strategy of incorporating the advantages of both conventional small molecules and polymers for OPVs

A Series of Simple Oligomer-like Small Molecules Based on Oligothiophenes for Solution-Processed Solar Cells with High Efficiency

A series of acceptor–donor–acceptor simple oligomer-like small molecules based on oligothiophenes, namely, DRCN4T–DRCN9T, were designed and synthesized. Their optical, electrical, and thermal properties and photovoltaic performances were systematically investigated. Except for DRCN4T, excellent performances were obtained for DRCN5T–DRCN9T. The devices based on DRCN5T, DRCN7T, and DRCN9T with axisymmetric chemical structures exhibit much higher short-circuit current densities than those based on DRCN6T and DRCN8T with centrosymmetric chemical structures, which is attributed to their well-developed fibrillar network with a feature size less than 20 nm. The devices based on DRCN5T/PC₇₁BM showed a notable certified power conversion efficiency (PCE) of 10.10% under AM 1.5G irradiation (100 mW cm^–2) using a simple solution spin-coating fabrication process. This is the highest PCE for single-junction small-molecule-based organic photovoltaics (OPVs) reported to date. DRCN5T is a rather simpler molecule compared with all of the other high-performance molecules in OPVs to date, and this might highlight its advantage in the future possible commercialization of OPVs. These results demonstrate that a fine and balanced modification/design of chemical structure can make significant performance differences and that the performance of solution-processed small-molecule-based solar cells can be comparable to or even surpass that of their polymer counterparts