Recent progress in computational exploration and design of functional materials

In this review, we summarize our work for the computational study and design of functional materials. Emphasis is laid on computational spectroscopy in the condensed phase as well as exploration of solar light-driven water splitting. In particular, dynamic ab initio methods have been in the focus of recent developments. This has enabled computationally efficient access to spectroscopic signatures, local properties, and innovative analysis of complex systems. Examples involve periodic subsystem density functional theory and density functional perturbation theory as well as (vibrational) spectroscopy such as Raman (optical activity) spectroscopy or sum frequency generation for in-depth study of interfaces. In addition, sophisticated approaches for exploration of water splitting processes are outlined, especially for water oxidation as one of the limiting factors for efficient water splitting devices. In-depth study of water oxidation mechanisms and related reaction networks in combination with (dynamic) consideration of environmental effects has allowed unprecedented new insight and discovery of essential factors influencing water oxidation behaviour, thus paving the way for novel design approaches for more efficient catalysts

Robust ΔSCF calculations with direct energy functional minimization methods and STEP for molecules and materials

The direct energy functional minimization method using the orbital transformation (OT) scheme in the program package CP2K has been employed for Δ self-consistent field (ΔSCF) calculations. The OT method for non-uniform molecular orbitals occupations allows us to apply the ΔSCF method for various kinds of molecules and periodic systems. Vertical excitation energies of heteroaromatic molecules and condensed phase systems, such as solvated ethylene and solvated uracil obeying periodic boundary conditions, are reported using the ΔSCF method. In addition, a Re–phosphate molecule attached to the surface of anatase (TiO2) has been investigated. Additionally, we have implemented a recently proposed state-targeted energy projection ΔSCF algorithm [K. Carter-Fenk and J. M. Herbert, J. Chem. Theory Comput. 16(8), 5067–5082 (2020)] for diagonalization based SCF in CP2K. It is found that the OT scheme provides a smooth and robust SCF convergence for all investigated excitation energies and (non-)periodic systems

Determination of pKa Values via ab initio Molecular Dynamics and its Application to Transition Metal-Based Water Oxidation Catalysts

The pKa values are important for the in-depth elucidation of catalytic processes, the computational determination of which has been challenging. The first simulation protocols employing ab initio molecular dynamics simulations to calculate pKa values appeared almost two decades ago. Since then several slightly different methods have been proposed. We compare the performance of various evaluation methods in order to determine the most reliable protocol when it comes to simulate pKa values of transition metal-based complexes, such as the here investigated Ru-based water oxidation catalysts. The latter are of high interest for sustainable solar-light driven water splitting, and understanding of the underlying reaction mechanism is crucial for their further development

Vibrational spectroscopy by means of first-principles molecular dynamics simulations

Vibrational spectroscopy is one of the most important experimental techniques for the characterization of molecules and materials. Spectroscopic signatures retrieved in experiments are not always easy to explain in terms of the structure and dynamics of the studied samples. Computational studies are a crucial tool for helping to understand and predict experimental results. Molecular dynamics simulations have emerged as an attractive method for the simulation of vibrational spectra because they explicitly treat the vibrational motion present in the compound under study, in particular in large and condensed systems, subject to complex intramolecular and intermolecular interactions. In this context, first-principles molecular dynamics (FPMD) has been proven to provide an accurate realistic description of many compounds. This review article summarizes the field of vibrational spectroscopy by means of FPDM and highlights recent advances made such as the simulation of Infrared, vibrational circular dichroism, Raman, Raman optical activity, sum frequency generation, and nonlinear spectroscopies

On the vibrations of formic acid predicted from first principles

In this article, we review recent first principles, anharmonic studies on the molecular vibrations of gaseous formic acid in its monomer form. Transitions identified as fundamentals for both cis- and trans form reported in these studies are collected and supported by results from high-resolution experiments. Attention is given to the effect of coordinate coupling on the convergence of the computed vibrational states

Automatic purpose-driven basis set truncation for time-dependent Hartree–Fock and density-functional theory

Real-time time-dependent density-functional theory (RT-TDDFT) and linear response time-dependent density-functional theory (LR-TDDFT) are two important approaches to simulate electronic spectra. However, the basis sets used in such calculations are usually the ones designed mainly for electronic ground state calculations. In this work, we propose a systematic and robust scheme to truncate the atomic orbital (AO) basis set employed in TDDFT and TD Hartree–Fock (TDHF) calculations. The truncated bases are tested for both LR- and RT-TDDFT as well as RT-TDHF approaches, and provide an acceleration up to an order of magnitude while the shifts of excitation energies of interest are generally within 0.2 eV. The procedure only requires one extra RT calculation with 1% of the total propagation time and a simple modification on basis set file, which allows an instant application in any quantum chemistry package supporting RT-/LR-TDDFT calculations. Aside from the reduced computational effort, this approach also offers valuable insight into the effect of different basis functions on computed electronic excitations and further ideas on the design of basis sets for special purposes

Advancing Computational Approaches for Study and Design in Catalysis

Our group deals with the development of computational methods and their application to complex systems and processes. Emphasis is laid on accurate approaches derived from quantum mechanics, which we have used to investigate challenging questions in an interdisciplinary field encompassing chemistry, biology, physics, and materials science. In this review, we describe our recent activities for advancing computational approaches in catalysis. Moreover, our work for the study and design of catalysts for solar light-driven water splitting is summarized. The latter is a promising approach to face the world's increasing demand for sustainable energy storage and conversion. Emphasis is put on forefront methods for highly accurate electronic structure, sophisticated inclusion of environmental and dynamic effects and the derivation of structure–activity relationships for informed in silico design. This paves the way for the development of more efficient catalysts in close collaboration with experimental groups

Localized molecular orbitals for calculation and analysis of vibrational Raman optical activity

We present a novel method for the calculation of vibrational Raman optical activity (ROA) spectra based on localized molecular orbitals. This allows to split total ROA intensities into contributions of subsets, which can be chosen flexibly depending on the question of interest. It provides an appealing way to gain deeper insight into the factors influencing chirality and associated bands observed in the spectrum. As example, the ROA spectrum of a tryptophan model system, in particular the band arising from its W3 vibration, has been investigated

The photodissociation of solvated cyclopropanone and its hydrate explored via non-adiabatic molecular dynamics using ΔSCF

The decay of cyclopropanone is a typical example of a photodecomposition process. Ethylene and carbon monoxide are formed following the excitation to the first singlet excited state through a symmetrical or asymmetrical pathway. The results obtained with non-adiabatic molecular dynamics (NAMD) using the delta self-consistent field (ΔSCF) method correspond well to previous experimental and multireference theoretical studies carried out in the gas phase. Moreover, this efficient methodology allows NAMD simulations of cyclopropanone in aqueous solution to be performed, which reveal analogue deactivation mechanisms, but a shorter lifetime and reduced photodissociation as compared to the gas-phase. The excited state dynamics of cyclopropanone hydrate, an enzyme inhibitor, in an aqueous environment are reported as well. Cyclopropanone hydrate strongly interacts with the surrounding solvent via the formation of hydrogen bonds. Excitation to the first singlet excited state shows an asymmetric pathway with cyclopropanone hydrate and propionic acid as the main photoproducts