Magnetic circular dichroism (MCD) spectra are able to provide insights into the geometric, electronic, and magnetic properties of chemical systems. However, they can be challenging to understand and simulate given the need to simultaneously treat both the finite magnetic and optical fields. Thus, efficient simulations are desired to understand the spectra and resolve the molecular electronic states. Real-time dynamics are used widely in the simulation of electronic spectroscopies such as absorption as well as electronic circular dichroism, but simulating MCD with real-time dynamics is technically and theoretically challenging. In this work, we introduce a real-time dynamics-based ab initio method with a nonperturbative treatment of a static magnetic field with London orbitals for simulating the MCD spectra of closed shell systems. Effects of a magnetic field are included variationally in the spin-free nonrelativistic Hamiltonian. Real-time time-dependent density functional theory dynamics are then performed, from which we compute the response function in the presence of the external magnetic field, giving the MCD spectrum. The method developed in this paper is applied to simulate the MCD spectra for pyrimidine, pyrazine, and 1,4-naphthoquinone. Results are discussed and compared to the experiment.

The development of color centers in diamond as the basis for emerging quantum technologies has been limited by the need for ion implantation to create the appropriate defects. We present a versatile method to dope diamond without ion implantation by synthesis of a doped amorphous carbon precursor and transformation at high temperatures and high pressures. To explore this bottom-up method for color center generation, we rationally create silicon vacancy defects in nanodiamond and investigate them for optical pressure metrology. In addition, we show that this process can generate noble gas defects within diamond from the typically inactive argon pressure medium, which may explain the hysteresis effects observed in other high-pressure experiments and the presence of noble gases in some meteoritic nanodiamonds. Our results illustrate a general method to produce color centers in diamond and may enable the controlled generation of designer defects.

Developing interfacial probes of ligand–nanocluster interactions is crucial for understanding and tailoring the optoelectronic properties of these emerging nanomaterials. Using transient IR spectroscopy, we demonstrate that ligand vibrational modes of oleate-capped 1.3 nm InP nanoclusters report on the photogenerated exciton. The exciton induces an intensity change in the asymmetric carboxylate stretching mode by 57% while generating no appreciable shift in frequency. Thus, the observed difference signal is attributed to an exciton-induced change in the dipole magnitude of the asymmetric carboxylate stretching mode. Additionally, the transient IR data reveal that the infrared dipole change is dependent on the geometry of the ligand bound to the nanocluster. The experimental results are interpreted using TDDFT calculations, which identify how the spatial dependence of an exciton-induced electron density shift affects the vibrational motion of the carboxylate anchors. More broadly, this work demonstrates transient IR spectroscopy as a useful method for characterizing ligand–nanocluster coupling interactions.

The presence of mid-gap states introduced by localized defects in wide-band-gap doped semiconductors can strongly affect the electronic structure and optical properties of materials, generating a wide range of applications. Silicon-divacancy defects in diamond have been recently proposed for probing high-resolution pressure changes and performing quantum cryptography, making them good candidates to substitute the more common nitrogen-vacancy centers. Using group theory and ab initio electronic structure methods, the molecular origin of mid-gap states, zero phonon line splitting and size dependence of the electronic transitions involving the SiV center is investigated in this work. The effects of localized defects on the Raman vibrational and carbon K-edge X-ray absorption spectra are also explored for nanodiamonds. This paper presents an important analysis of the electronic and vibrational structure of nanosized semiconductors in the presence of mid-gap states due to localized defects, providing new insights into possible mechanisms for modulating their optical properties.

Diamonds approaching the nanoscale have the potential for use as probe materials as their optical properties can be sensitive to optical/electric fields, mechanical stress/ pressure, and the configuration of nuclear spins. The surface of nanodiamonds impacts their optical properties and sensing capabilities, and examining the nanodiamond surface through X-ray absorption can give insights into molecular surface structures. Here, quantum dot models with varying amounts of surface carbon passivation are prepared, optimized, and compared. The loss of the diamond sp 3 lattice is examined by investigating the bond length and tetrahedral character of the carbons comprising nanodiamonds for the appearance of aromatic sp 2 surface domains. Electronic transitions in the carbon K-edge region, using the energy-specific time-dependent density functional theory method, as well as vibrational spectra are computed from the optimized models. The surface reorganization is shown to affect the electronic characteristics of the nanodiamond. As a result, there is a distinct absorption peak in the carbon K-edge region, along with stretching modes in the vibrational spectra, that can be correlated to the nature of the surface hybridization of the nanodiamond.