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The elaborate configuration of the heterostructure is crucial and challenging to achieve high solar-to-hydrogen efficiency or CO2 reduction efficiency .

The thermoelectric performance of the CuSbS2 monolayer is determined using the relaxation times obtained from electron–phonon coupling calculations and the transport properties of phonons and electrons.

Through increasing the volume of fullerene and embedding alkali metal ions, we could enhance intermolecular interactions and intermolecular CT significantly, thereby improving the second-order NLO properties of CT complexes.

Formation of organic co-crystals is an effective strategy to synthesize near infrared emission and nonlinear optical (NLO) materials, which often show "1 + 12" performance. Moreover, the crystallization process can be effectively regulated through supramolecular interactions; thus the properties of co-crystal materials can also be flexibly regulated. Here, in order to further understand the nature and formation mechanism of co-crystals from the perspective of theoretical research, we studied the structures, intermolecular interactions, absorption spectra, charge transfer (CT) characteristics and nonlinear optical (NLO) properties of the newly synthesized organic co-crystals formed between naphthalenediimide based triangles (NDI, acceptor) and coronene (COR, donor). According to the analysis of decomposition of intermolecular interaction energy, dispersion energy played a major role, so the co-crystal properties can be regulated by regulating the intermolecular dispersion energy. More importantly, the formation of co-crystals NDI-COR and NDI-2COR reduced the

The feasibility and efficiency of photocatalytic solar-energy-to-hydrogen conversion via a direct Z-scheme driven by a HfS2/SiSe heterostructure are investigated by employing first-principles hybrid functional theory.

We investigated the ultrafast photoisomerization of N-(2-methoxybenzylidene)aniline in the gas phase excited into the second singlet (S2) state by nonadiabatic surface-hopping dynamics calculations. Two trans isomers (1E and 1E') were taken into consideration in our dynamics simulation. Three conical intersections (CIs) were characterized in the optimization. The CI between S2 and the first singlet (S1) states presents a nearly planar structure, while the other two CIs (CItwist-I and CItwist-II) between S1 and the ground (S0) states show nearly perpendicular geometries. After two trans isomers excited to the S2 state, the torsion of the C-N bond connected the phenyl group and the stretch of the central bridging bond make the molecule reach CIplanar, and the S2/S1 hopping occurs. During the S1-state dynamics, the molecule moves to a S1/S0 CI (CItwist-I or CItwist-II) by the rotation of the central bridging bond. The cis isomer is obtained through a barrierless pathway in the S0 state with the torsion of the three bridging bonds. There is a main channel and an alternative one for the photoisomerization process of both trans isomers. CItwist-I and CItwist-II act as S1/S0 decay funnels in the main isomerization channels of 1E and 1E' isomers, respectively, and the photochemical processes of 1E and 1E' lead to different cis isomers.

The potential astronomical interest dithioformic acid (trans-HC(=S)SH) exists five isomers and has received considerable attention of astronomical observation in recent years. The different positions of H atoms of five isomers lead to diverse point groups, dipole moments, and spectroscopic constants. The anharmonic force field and spectroscopic constants of them are calculated using CCSD(T) and B3LYP employing correlation consistent basis sets. Molecular structures, dipole moments, rotational constants, and fundamental frequencies of trans-HC(=S)SH are compared with the available experimental data. The B3LYP/Gen=5 and CCSD(T)/Gen=Q results can reproduce them well. Molecular structures, dipole moments, relative energies, spectroscopic constants of cis-HC(=S)SH and dithiohydroxy carbene (DTHC) are also calculated. The new data obtained in this study are expected to guide the future high resolution experimental work and to assist astronomical search for CH2S2.

Direct laser cooling is a very promising method to obtain cold molecules for various applications. However, a molecule with satisfactory electronic and optical properties for the optical scheme is difficult to identify. By suggesting criteria for the qualified molecules, we develop a method to identify the suitable polyatomic molecules for direct laser cooling. The new criteria from the equilibrium geometrical structures and fundamental frequencies of the ground and low-lying excited states are used to replace the past ones based on Franck–Condon factors. The new method can rapidly identify the preferable one among many candidate polyatomic molecules based on ab initio calculations because the new criteria are free from the construction of potential energy surfaces. The method is testified by using triatomic molecules containing OH. All the reported and two new molecules suitable for direct laser cooling are identified by comparing 168 electronic states of 28 molecules with the new criteria. The newly found molecules have been confirmed using the Franck–Condon factors from the construction of potential energy surfaces. Finally, the optical schemes for the direct laser cooling of the SOH and SeOH molecules are established.

Two-dimensional (2D) heterostructures with the Z-scheme can significantly improve the recombination of the photogenerated charge pairs and increase the overpotential compared with the corresponding monolayers. Based on first-principles calculations, we demonstrate the photocatalytic performance with the Z-scheme of three 2D AuSe/SnS heterostructures identified from nine stacking types of AuSe and SnS monolayers using their formation energies. The thermal stabilities of the chosen heterostructures are assured by molecular dynamics simulations. The band alignment and built-in electric field support the heterostructures to drive the photocatalytic hydrogen and oxidation evolution reactions with the direct Z-scheme. Moreover, the optical absorption of both AuSe and SnS monolayers is obviously observed in the visible light and UV ranges, indicating their excellent response to solar light. The highest solar-to-hydrogen energy conversion efficiency of the heterostructures can reach 23.96%. The change in Gibbs free energy in the hydrogen evolution reaction with the heterostructures is in the range of 0.63–0.97 eV, indicating that these reactions are not difficult to carry out. Therefore, the present AuSe/SnS heterostructures could be promising candidates for producing hydrogen from photocatalytic water splitting with the Z-scheme driven by solar light.

In the formation of noncovalent complexes, the stacking arrangements of corannulene and fullerene are diverse, most of which are combinations of multiple corannulenes and fullerene. Here, a composition ratio of 2 : 1 was selected for the complex between corannulene and fullerene (C60 and C70) to investigate the effects of different superposition modes, including concave–convex and convex–convex interactions, on the stability and third-order nonlinear optical (NLO) properties of the composite materials. It was found that the concave–convex interaction was stronger and it was reported to stabilize the charge-transfer (CT) complex more effectively than the convex–convex interaction. The dispersion range of the concave–convex interaction was larger than that of the convex–convex interaction, which is consistent with the interaction energy results. The packing design with the double convex–convex interactions exhibited the largest linear optical response and third-order NLO response, which showed that the convex–convex interaction was more likely to be excited and cause intermolecular CT as compared to the concave–convex interaction. This work confirmed that the packing arrangement significantly affected the NLO response and will advance the development of NLO crystals.

A slit structure consisted of two bending graphene membranes is built as a nano check valve theoretically. Molecular dynamics simulations are used to investigate the opening and closing of this check valve. The backflow through the valve are also studied. The results show that the check valve can maintain the unidirectional flow of fluid and prevent backflow within the appropriate pressure range. Specifically, the opening and closing pressure of the valve are 148.2 and 24.6 MPa, respectively. The maximum working pressure of the check valve should be lower than 197.6 MPa. Moreover, the water passing rate is larger at a higher pressure due to the larger slit width and water flux. This check valve is expected to have many potential applications in the nanofluidic field.

The feasibility of SiI2 monolayer as the candidate for photocatalytic water splitting for hydrogen generation under the irradiation of the solar light is explored. The geometrical structure, the electronic and optical properties, the mobility of carrier and strain engineering of the monolayer are investigated based on the first-principles calculations. The results demonstrate SiI2 monolayer possesses an indirect gap of 2.33 eV (HSE06), and both the band edge and the bandgap match the redox potential conditions of the water splitting for hydrogen generation. There is an obvious optical absorption in the visible light and near-ultraviolet region and can be enhanced by the compressive strain. Moreover, the mobility of the electron is significantly different from that of the hole, implicating that the effective spatial charge separation is expectable and the ratio of the recombination of the photogenerated charge pairs is low. The primary adsorption site of the water molecule is identified. The Gibbs free energy and the adsorption energies are calculated to demonstrate the H2 generation from the water molecule splitting on the monolayer. All the considered properties support that SiI2 monolayer can be achieved as a promising candidate for the photocatalytic water splitting for hydrogen production under the irradiation of the solar light.

As influence factors in generating third-order nonlinear optical (NLO) responses, several parameters, including the length of π-conjugated linkers, donor/acceptor substituents, and shape of the π e...

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

The application of organic conjugated molecular systems to photocatalysis is based on the charge transition with different electronegative substituents and the electron–hole separation behavior of charge transfer under light excitation. In this work, the relationship between the intra-molecular electrical field and molecular second-order nonlinear optical properties is investigated theoretically by the sum-of-states (SOS) method. We use substituents with different electron affinity energy to construct internal electric fields with different properties in similar conjugated systems. The studies of these systems reveal the intra-molecular electric field strength and mode regulation of nonlinear optical coefficients and explain its physical mechanism. The intra-molecular charge recombination caused by the electrostatic potential multipole field of different substituents changes the transition behavior of one-photon, resulting in the enhancement of nonlinear optical properties (second-harmonic generation and sum-frequency coefficient) greater than 104.

The curved and electron-rich nature of buckybowls doped with heteroatoms makes them suitable electron-donating hosts for fullerene in the formation of concave–convex supramolecular complexes. The bowl depths of heteroatom-doped buckybowls are sensitive for the radius of the doping atoms. With the aim to investigate the influence of the bowl depth of the buckybowl and intermolecular interaction on the nonlinear optical (NLO) responses of complexes, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities (βtot) of the complexes formed by X-doped sumanene (X= Si, Ge, O, S, and Se) and C60 have been explored using density functional theory calculations. It is found that as doped atoms’ radii increase, the curvatures with shallower bowl depth of buckybowls and the distance between the base of C60 and buckybowls become increasingly smaller. However, atoms with larger radius tend to produce stronger binding energies between buckybowls and C60, accompanied with a gradu...

Tetraphenylporphyrin (TPP) has been reported as the sensitizer of the dye-sensitized solar cells (DSSC). However, the efficiency is unsatisfactory because of the unobvious visible light absorption. Here we examine the improvement of the efficiency by using a sensitizer of cir-coronene graphene oxide quantum dot (GOQD) and TPP composite. The geometrical structures of the GOQD-TPP nanocomposites, as well as their separate components, are fully optimized by employing the first-principles density functional theory (DFT). The frequency analysis is used to confirm the energy stability of the obtained structures and time-dependent DFT (TDDFT) is used for the calculations of the optical absorption. We use the I−/I3− electrolyte, and the conduction band minimum of TiO2 electrode as the example to examine the feasibility of the nanocomposites as the sensitizer of DSSC by evaluating the energy levels, the charge spatial separation of the frontier molecular orbitals and electron transfer of the nanocomposites. The results demonstrate that the GOQD(18OH)-TPP can meet the necessary conditions of the sensitizer of DSSC. Besides, the most favorable is because of its larger driving force and light-harvesting efficiency, the suitable open-circuit voltage value, and enhancement light absorption. The results implicate that this one is the most promising sensitizer candidate of DSSC. These findings can provide a useful reference for developing the sensitizer of DSSC or designing the materials to harvest solar energy based on the nanocomposites of GOQD-TPP.

The synthesis of AgIn5Te8 is realized and the thermoelectric properties dependent on temperature is examined. However, the mechanism remains unclear and the synergistic effect of the temperature and the carrier concentration on thermoelectric properties is not explored. Here, the electronic transport properties are calculated by using the first-principles density functional theory combined with the semi-classical Boltzmann transport theory. The relaxation time is estimated by the deformation potential theory. The lattice thermal conductivity is evaluated by the Slack’s model, and the result is in good agreement with the experimental value. High anisotropic behavior is identified for the thermal and electronic transport properties, which supports the experimental observation. By tuning the carrier concentration and temperature, a maximum thermoelectric figure of merit of 2.28 can be achieved for p-type AgIn5Te8 in xx direction. The present results provide insight into the thermoelectric properties of AgIn5Te8 and a guide to prepare thermoelectric materials with AgIn5Te8.

Nonadiabatic dynamics of a nonplanar green fluorescent protein (GFP) chromophore derivative was examined theoretically by trajectory surface hopping approach at the CASSCF level based on Zhu-Nakamura theory. The geometry optimizations show that there are four ground-state minima and four conical intersections between the ground (S0) and first excited (S1) states. Four S1-state minima were found at a perpendicularly twisted conformation around the imidazolinone-bridged bond. Upon excitation to S1 state, the main decay pathways of four isomers involve different S0/S1 potential energy surface conical intersections. The dominant excited-state relaxation mechanism of this GFP chromophore derivative is the twists of two bridging bonds and the methyl group in the bridge combined with the pyramidalization character of the central carbon atom. Further twists of two bridging bonds and the methyl group occur sequentially in the S0 state. It is worth to mention that the special volume-conserving motion of this molecule is attributed to twists of two bridging bonds in the same direction during the whole photoisomerization processes. The theoretical investigation presented herein provides important insights into the volume-conserving photoisomerization mechanisms of a nonplanar GFP chromophore derivative. We believe that the present work can benefit the design of the photochromic molecule devices in confined media.

To evaluate the feasibility of the laser cooling of CuH molecule, we investigate the electronic properties, the vibrational and rotational characteristics of the molecule based on the multi-reference configuration interaction method with all-electron basis sets. The potential energy curves (PECs) of X1Σ+, A1Σ+, B1Σ+, a3Σ+, b3Σ+, e3Σ+, C1П, D1П, c3П and d3П states and the transition dipole moments between these states are calculated. The Schrodinger equation of nuclear movement is solved for each electronic state to obtain the rotational and vibration energy levels. The spectroscopic parameters are calculated based on the fitted analytical function from the PECs. The present results are in good agreement with the theoretical and experimental values available in the literature. The optical scheme of the laser cooling for CuH molecule is constructed with A1Σ+ ↔ X1Σ+ as the close-loop transition. Three lasers are necessary in each direction to maintain enough scattering photons because of the limited Franck-Condon factor of 0.78. The wavelengths of the pumping lasers are determined. The recoil temperature is 1.72 μk, which is the expected temperature to be reached through the method of the cooling below the doppler limit.

Based on the first principles calculations, the feasibility of the photocatalytic hydrogen production from water splitting driven by N-doped β-Ga2O3 in the visible light is investigated. The formation energy and dynamics properties are used to examine the stability of the doped structures. The absolute positions of the band energy edges are obtained and compared to the redox potentials of the hydrogen production reaction. Moreover, we calculate the carrier lifetime and mobility for both electron and hole of all the considered structures. The optical absorption is also calculated for each structure. The results show that the 5.00 at.% N-doped β-Ga2O3 has the satisfactory band energy edges, obvious difference of mobilities between electron and hole, and significant enhancement of absorption in visible light range, indicating it is a promising photocatalytic material to catalyze hydrogen production from water splitting under the irradiation of the visible light.

The pristine BaTiO3 has been experimentally confirmed to catalyze hydrogen production from water splitting, but the reaction cannot be driven by the visible light because of the wide energy band gap of BaTiO3. To understand the feasibility of the reaction driven by the visible light of the strongest part of the solar energy, we have investigated the effect of different concentrations of oxygen group element dopants on the electronic and optical properties of BaTiO3 by using first-principles density functional theory calculations with meta-GGA + MBJ potential. The formation energy of each doped structure is calculated to examine the feasibility of synthesis in energy. The energy band gaps and the energy positions of conduction and valence bands are calculated and the results reveal that all the structures except the one that doped with 5 at% Te satisfy the conditions of water splitting although the energy band gaps of the doped BaTiO3 decrease obviously. The partial charge distributions of conduct band maximum and valence band minimum are used to demonstrate the electron-hole separation. The absorption coefficients are calculated for all the considered structures. The results demonstrate that the doped chalcogens can significantly enhance the absorption in visible light range, which implies that the doped BaTiO3 are promising to catalyze the hydrogen production from water splitting driven by solar energy.

A 2D ZrI2 monolayer with a high dimensionless figure of merit ( ZT) is analyzed in terms of intrinsic carrier concentrations, transport coefficients, and a bipolar effect. The ZrI2 monolayer with a space group of P21/ m is fully optimized. The dynamic and thermal stabilities are verified by computing the phonon dispersion in addition to performing ab initio molecular dynamics simulation. The thermal conductivity of the lattice is evaluated by employing the phonon Boltzmann transport theory and the first-principle second and third force constants. The Seebeck coefficients, electronic thermal conductivities, and electric conductivities of the monolayer are determined by solving the relaxation time approximation semiclassical Boltzmann transport equation. To further explore the chance for promoting ZT, we investigate the manipulating effect of the carrier concentrations. The largest ZT with the bipolar effect can reach 7.86 at 700 K, implying that the ZrI2 monolayer has excellent thermoelectric performance.

The geometrical configurations of the XBiSe

Constructing a van der Waals heterostructure is a practical way to promote the conversion efficiency of solar energy. Here, we demonstrate the efficient performance of a GeSe/AsP heterostructure in solar energy cells based on the first-principles calculations. The electronic properties, optical absorption, and optoelectronic properties are calculated to evaluate the efficiency of the newly designed heterostructure. The results indicate that the GeSe/AsP heterostructure possesses a type-II band alignment with an indirect bandgap of 1.10 eV, which greatly promotes the effective separation of photogenerated carriers. Besides, an intrinsic electric field is formed in the direction from the AsP to GeSe monolayer, which is beneficial to prevent the recombination of the photogenerated electron-hole pair. Simultaneously, a strong optical absorption is observed in the visible light range. The predicted power conversion efficiency (PCE) of the GeSe/AsP heterostructure is 16.0% and can be promoted to 17.3% by applying 1% biaxial compression strain. The present results indicate that the GeSe/AsP heterostructure is a promising candidate material for high-performance solar cells.

Two-dimensional (2D) materials of SiMI