The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

Synthesis and Characterization of Molybdenum Back Contact Using Direct Current-Magnetron Sputtering for Thin Film Solar Cells

In present work, we report synthesis of molybdenum (Mo) thin films by direct current (DC)-magnetron sputtering method. The structural, optical, morphological, and electrical properties were investigated as a function of target-to-substrate distance. From the results, it is evident that with increase in target-to-substrate distance the thickness of films decreases while its sheet resistance and electrical resistivity increases, which is confirmed by van der Pauw method. Low angle XRD analysis revealed that with increase in target-to-substrate distance preferred orientation of Mo crystallites changes from (211) to (110) and its size decreases. The field emission scanning electron microscope (FE-SEM) analysis revealed a significant change in surface morphology with increase in target-to-substrate distance. UV-Visible spectroscopy analysis showed that Mo films deposited at higher target-to-substrate distance have more reflection than those deposited at lower target-to-substrate. Finally, adhesion test was performed using scotch hatch tape adhesion test which show all Mo films have excellent adhesion over the entire range of target-to-substrate distance studied. The employment of such Mo films as back contact can be useful to improve efficiency of CZTS solar cells

Spin State Ordering in Metal-Based Compounds Using the Localized Active Space Self-Consistent Field Method

Quantitatively accurate calculations for spin state ordering in transition-metal complexes typically demand a robust multiconfigurational treatment. The poor scaling of such methods with increasing size makes them impractical for large, strongly correlated systems. Density matrix embedding theory (DMET) is a fragmentation approach that can be used to specifically address this challenge. The single-determinantal bath framework of DMET is applicable in many situations, but it has been shown to perform poorly for molecules characterized by strong correlation when a multiconfigurational self-consistent field solver is used. To ameliorate this problem, the localized active space self-consistent field (LASSCF) method was recently described. In this work, LASSCF is applied to predict spin state energetics in mono- and di-iron systems and we show that the model offers an accuracy equivalent to CASSCF but at a substantially lower computational cost. Performance as a function of basis set and active space is also examined.</p

Localized Active Space State Interaction: A Multireference Method For Chemical Insight

Multireference electronic structure methods, like the complete active space (CAS) selfconsistent field model, have long been used to characterize chemically interesting processes. Important work has been done in recent years to develop modifications having lower computational cost than CAS, but typically these methods offer no more chemical insight than that from the CAS solution being approximated. In this paper, we present the localized active space - state interaction (LASSI) method that can be used not only to lower the intrinsic cost of the multireference calculation, but also to improve interpretability. The localized active space (LAS) approach utilizes the local nature of electron-electron correlation to express a composite wave function as an antisymmetrized product of unentangled wave functions in local active subspaces. LASSI then uses these LAS states as a basis from which to express complete molecular wave functions. This not only makes the molecular wave function more compact, but it also permits flexibility in choosing those states to include in the basis. Such selective inclusion of states translates to selective inclusion of specific types of interactions, thereby allowing a quantitative analysis of these interaction. We demonstrate the use of LASSI to study charge migration and spin-flip excitations in multireference organic molecules. We also compute the J coupling parameter for a bimetallic compound using various LAS bases to construct the Hamiltonian to provide insight into the coupling mechanism

Localized Active Space Pair-Density Functional Theory

Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. In previous work, we have shown that the localized active space (LAS) self-consistent field (SCF) method is an efficient way to obtain multi-configuration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration pair-density functional theory (PDFT), which calculates the energy based on the density and on-top pair density obtained from a multiconfiguration wave function. In this work we introduce localized-active-space pair-density functional theory, which uses a LAS wave function for subsequent PDFT calculations. The method is tested for computing spin-state energy gaps in conjugated organic molecules and bimetallic compounds and is shown to give results within 0.05 eV of the corresponding CAS-PDFT results at a significantly lower cost

Synthesis and characterization of molybdenum back contact using direct current-magnetron sputtering for thin film solar cells

In present work, we report synthesis of molybdenum (Mo) thin films by direct current (DC)-magnetron sputtering method. The structural, optical, morphological, and electrical properties were investigated as a function of target-to-substrate distance. From the results, it is evident that with increase in target-to-substrate distance the thickness of films decreases while its sheet resistance and electrical resistivity increases, which is confirmed by van der Pauw method. Low angle XRD analysis revealed that with increase in target-to-substrate distance preferred orientation of Mo crystallites changes from (211) to (110) and its size decreases. The field emission scanning electron microscope (FE-SEM) analysis revealed a significant change in surface morphology with increase in target-to-substrate distance. UV-Visible spectroscopy analysis showed that Mo films deposited at higher target-to-substrate distance have more reflection than those deposited at lower target-to-substrate. Finally, adhesion test was performed using scotch hatch tape adhesion test which show all Mo films have excellent adhesion over the entire range of target-to-substrate distance studied. The employment of such Mo films as back contact can be useful to improve efficiency of CZTS solar cells

Localized Quantum Chemistry on Quantum Computers

Quantum chemistry calculations of large, strongly correlated systems are typically limited by the computation cost that scales exponentially with the size of the system. Quantum algorithms, designed specifically for quantum computers, can alleviate this, but the resources required are still too large for today’s quantum devices. Here, we present a quantum algorithm that combines a localization of multireference wave functions of chemical systems with quantum phase estimation (QPE) and variational unitary coupled cluster singles and doubles (UCCSD) to compute their ground-state energy. Our algorithm, termed “local active space unitary coupled cluster” (LAS-UCC), scales linearly with the system size for certain geometries, providing a polynomial reduction in the total number of gates compared with QPE, while providing accuracy above that of the variational quantum eigensolver using the UCCSD ansatz and also above that of the classical local active space self-consistent field. The accuracy of LAS-UCC is demonstrated by dissociating (H2)2 into two H2 molecules and by breaking the two double bonds in trans-butadiene, and resource estimates are provided for linear chains of up to 20 H2 molecules

Electrochemical synthesis of p-Cu2O/n-ZnO nanorods hetero-junction for photovoltaic application

Development of high performance visible light responsive solar cell materials has attracted wide interest due to their potential applications in the energy industries. In this work, ZnO nanorods films were successfully prepared on the ITO coated glass substrates via simple three electrode electrochemical deposition route. The Cu2O nanoparticles were then electrodeposited on the surface of ZnO nanorods to form p-Cu2O/n-ZnO core-shell hetero-structure. The synthesized ZnO, Cu2O films and p-Cu2O/n-ZnO hetero-structure were characterized by low angle x-ray diffraction, scanning electron microscopy, and UV-Visible spectrophotometer. Due to the hierarchical morphologies and core-shell structure, p-Cu2O/n-ZnO hetero-structure shows a prominent visible-light-driven photocatalytic performance under the low intensity light irradiation. The obtained results suggest that it is possible to synthesize ZnO nanorods, Cu2O films and p-Cu2O/n-ZnO core-shell hetero-structure by a simple, cost effective and environment friendly electrodeposition process which can be useful for water splitting and solar cell device fabrication

Synthesis and characterization of DC magnetron sputtered nano structured molybdenum thin films

Molybdenum (Mo) thin films were deposited on corning glass (#7059) substrates using DC magnetron sputtering system. The effect of substrate temperature on the structural, morphology and topological properties have been investigated. Films were characterized by variety of techniques such as low angle x-ray diffraction (low angle XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM). The low angle XRD analysis revealed that the synthesized Mo films are nanocrystalline having cubic crystal structure with (110) preferential orientation. The microstructure of the deposited Mo thin films observed with FE-SEM images indicated that films are homogeneous and uniform with randomly oriented leaf shape morphology. The AFM analysis shows that with increase in substrate temperature the rms roughness of Mo films increases. The obtained results suggest that the synthesized nanostructured Mo thin films have potential application as a back contact material for high efficiency solar cells like CdTe, CIGS, CZTS etc