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Polymorphism is an issue troubling numerous scientific fields. A phenomenon where molecules can arrange in different orientations in a crystal lattice, polymorphism in the field of organic photovoltaic materials can dramatically change electronic properties of these materials. Rubrene is a benchmark photovoltaic material showing high carrier mobility in only one of its three polymorphs. To use rubrene in devices, it is important to quantify the polymorph distribution arising from a particular crystal growth method. However, current methods for characterizing polymorphism are either destructive or inefficient for batch scale characterization. Lattice phonon Raman spectroscopy has the ability to distinguish between polymorphs based on low frequency intermolecular vibrations. We present here the addition of microscopy to lattice phonon Raman spectroscopy, which allows us to not only characterize polymorphs efficiently and nondestructively through Raman spectroscopy but also concurrently gain information on the size and morphology of the polymorphs. We provide examples for how this technique can be used to perform large, batch scale polymorph characterization for crystals grown from solution and physical vapor transport. We end with a case study showing how Raman microscopy can be used to efficiently optimize a green crystal growth method, selecting for large orthorhombic crystals desired for rubrene electronic device applications.Our lives are surrounded by a rich assortment of disordered materials. In particular, glasses are well known as dense, amorphous materials, whereas gels exist in low-density, disordered states. Recent progress has provided a significant step forward in understanding the material properties of glasses, such as mechanical, vibrational, and transport properties. In contrast, our understanding of particulate physical gels is still highly limited. Here, using molecular dynamics simulations, we study a simple model of particulate physical gels, the Lennard-Jones (LJ) gels, and provide a comprehensive understanding of their structural, mechanical, and vibrational properties, all of which are markedly different from those of LJ glasses. First, the LJ gels show sparse, heterogeneous structures, and the length scale ξs of the structures grows as the density is lowered. Second, the LJ gels are extremely soft, with both shear G and bulk K moduli being orders of magnitude smaller than those of LJ glasses. Third, many low-frequency vibrational modes are excited, which form a characteristic plateau with the onset frequency ω* in the vibrational density of states. Structural, mechanical, and vibrational properties, characterized by ξs, G, K, and ω*, respectively, show power-law scaling behaviors with the density, which establishes a close relationship between them. Throughout this work, we also reveal that LJ gels are multiscale, solid-state materials (i) homogeneous elastic bodies at long lengths, (ii) heterogeneous elastic bodies with fractal structures at intermediate lengths, and (iii) amorphous structural bodies at short lengths.Present day computers do not have enough memory to store the high-dimensional tensors required when using a direct product basis to compute vibrational energy levels of a polyatomic molecule with more than about five atoms. One way to deal with this problem is to represent tensors using a tensor format. In this paper, we use the canonical polyadic (CP) format. Energy levels are computed by building a basis from vectors obtained by solving linear equations. The method can be thought of as a CP realization of a block inverse iteration method with multiple shifts. The CP rank of the tensors is fixed, and the linear equations are solved with an method. There is no need for rank reduction and no need for orthogonalization, and tensors with a rank larger than the fixed rank used to solve the linear equations are never generated. The ideas are tested by computing vibrational energy levels of a 64-D bilinearly coupled model Hamiltonian and of acetonitrile (12-D).We describe an updated algorithm for efficiently exploring structure-property spaces relating to physisorption of gases in porous materials. This algorithm uses previously described "pseudomaterials," which are crystals of randomly arranged and parameterized Lennard-Jones spheres, and combines it with a new iterative mutation exploration method. This algorithm is significantly more efficient at sampling the structure-property space than previously reported methods. For the sake of benchmarking to prior work, we apply this method to exploring methane adsorption at 35 bars (298 K) and void fraction as the main structure-property combination. We demonstrate the effect and importance of the changes that were required to increase efficiency over prior methods. The most important changes were (1) using "discrete" mutations less often, (2) decreasing degrees of freedom, and (3) removing biasing from mutations on bounded parameters.We present a rigorous framework for fully quantum calculation of the third dielectric virial coefficient Cɛ(T) of noble gases, including exchange effects. The quantum effects are taken into account with the path-integral Monte Carlo method. Calculations employing state-of-the-art pair and three-body potentials and pair polarizabilities yield results generally consistent with the few scattered experimental data available for helium, neon, and argon, but rigorous calculations with well-described uncertainties will require the development of surfaces for the three-body nonadditive polarizability and the three-body dipole moment. The framework, developed here for the first time, will enable new approaches to primary temperature and pressure metrology based on first-principles calculations of gas properties.A factorization of the matrix elements of the Dyall Hamiltonian in N-electron valence state perturbation theory allowing their evaluation with a computational effort comparable to the one needed for the construction of the third-order reduced density matrix at the most is presented. Thus, the computational bottleneck arising from explicit evaluation of the fourth-order density matrix is avoided. selleck inhibitor It is also shown that the residual terms arising in the case of an approximate complete active space configuration interaction solution and containing even the fifth-order density matrix for two excitation classes can be evaluated with little additional effort by choosing again a favorable factorization of the corresponding matrix elements. An analogous argument is also provided for avoiding the fourth-order density matrix in complete active space second-order perturbation theory. Practical calculations indicate that such an approach leads to a considerable gain in computational efficiency without any compromise in numerical accuracy or stability.In this work, we demonstrated an in situ approach for doping CsPbBr3 nanocrystals (NCs) with In3+ and Cl- with a ligand-assisted precipitation method at room temperature. The In3+ and Cl- co-doped NCs are characterized by the powder x-ray diffraction patterns, ultraviolet-visible, photoluminescence (PL) spectroscopy, time-resolved PL (TRPL), ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. Based on PL and TRPL results, the non-radiative nature of In3+-doping induced localized impurity states is revealed. Furthermore, the impact of In3+ and Cl- doping on charge transfer (CT) from the NCs to molecular acceptors was investigated and the results indicate that the CT at the interface of NCs can be tuned and promoted by In3+ and Cl- co-doping. This enhanced CT is attributed to the enlarged energy difference between relevant states of the molecular acceptor and the NCs by In3+ and Cl- upon co-doping. This work provides insight into how to control interfacial CT in perovskite NCs, which is important for optoelectronic applications.Photon upconversion, particularly via triplet-triplet annihilation (TTA), could prove beneficial in expanding the efficiencies and overall impacts of optoelectronic devices across a multitude of technologies. The recent development of bulk metal halide perovskites as triplet sensitizers is one potential step toward the industrialization of upconversion-enabled devices. Here, we investigate the impact of varying additions of bromide into a lead iodide perovskite thin film on the TTA upconversion process in the annihilator molecule rubrene. We find an interplay between the bromide content and the overall device efficiency. In particular, a higher bromide content results in higher internal upconversion efficiencies enabled by more efficient charge extraction at the interface likely due to a more favorable band alignment. However, the external upconversion efficiency decreases as the absorption cross section in the near infrared is reduced. The highest upconversion performance is found in our study for a bromide content of 5%. This result can be traced back to a high absorption cross section in the near infrared and higher photoluminescence quantum yield in comparison to the iodide-only perovskite and an increased driving force for charge transfer.In light of its ubiquitous presence in the interstellar gas, the chemistry and reactivity of the HCO+ ion requires special attention. The availability of up-to-date collisional data between this ion and the most abundant perturbing species in the interstellar medium is a critical resource in order to derive reliable values of its molecular abundance from astronomical observations. This work intends to provide improved scattering parameters for the HCO+ and He collisional system. We have tested the accuracy of explicitly correlated coupled-cluster methods for mapping the short- and long-range multi-dimensional potential energy surface of atom-ion systems. A validation of the methodology employed for the calculation of the potential well has been obtained from the comparison with experimentally derived bound-state spectroscopic parameters. Finally, by solving the close-coupling scattering equations, we have derived the pressure broadening and shift coefficients for the first six rotational transitions of HCO+ as well as inelastic state-to-state transition rates up to j = 5 in the 5-100 K temperature interval.Pyrene based molecules are inclined to form excimers through self-association upon photoexcitation. In this work, the pyrene core is functionalized with the N-methylacetamide group at the position 1 or 2 to develop pyren-1-methylacetamide (PyMA1) and pyren-2-methylacetamide (PyMA2), respectively. Upon photoexcitation with 345 nm, a portion of molecules in PyMA1 and PyMA2 solutions at ≥1.0 mM have formed static excimers. The steady state spectroscopic measurements suggest that, whether it is the dimerization of molecules in the ground state (GS) or in excimer formation, characteristic signs are more pronounced in PyMA1 than its isomeric counterpart, PyMA2. The shift of the excimer band in their respective emission spectra suggests that the extent of overlap in π-π stacking is greater for PyMA1 than for PyMA2 in the excited state. The optimized geometry of dimers in toluene shows that the overlapping area between the pyrene moieties in π-π stacking between the dimers is greater for PyMA1 than for PyMA2 in GS. The natural bond orbital analysis with the optimized GS geometries shows that the stabilization/interaction energy between the dimers in π-π stacking is higher in PyMA1 compared to PyMA2 in toluene.
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