Magnitude Of Coupling Research Articles

Increased localization of Majorana modes in antiferromagnetic chains on superconductors

Magnet-superconductor hybrid (MSH) systems are a key platform for custom-designed topological superconductors. Ideally, the ends of a one-dimensional MSH structure will host Majorana zero-modes (MZMs), the fundamental unit of topological quantum computing. However, some of the experiments with ferromagnetic chains show a more complicated picture. Due to tiny gap sizes and hence long coherence lengths MZMs might hybridize and lose their topological protection. Recent experiments on a niobium surface have shown that both ferromagnetic and antiferromagnetic chains may be engineered, with the magnetic order depending on the crystallographic direction of the chain. While ferromagnetic chains are well understood, antiferromagnetic chains are less so. Here we study two models inspired by the niobium surface: a minimal model to elucidate the general topological properties of antiferromagnetic chains, and an extended model to more closely simulate a real system by mimicking the proximity effect. We find that in general for antiferromagnetic chains the topological gap is larger than for ferromagnetic ones and thus coherence lengths are shorter for antiferromagnetic chains, yielding more pronounced localization of MZMs in these chains. While topological phases for both ferromagnetic and antiferromagnetic chains both depend on the magnetic moment of the adatoms and the chemical potential, we find that antiferromagnetic chains also have a strong dependence on the magnitude of Rashba spin-orbit coupling at the surface.

Origin of Ferromagnetic Exchange Coupling in Donor–Acceptor Biradical Analogues of Charge-Separated Excited States

A new donor-acceptor biradical complex, TpCum,MeZn(SQ-VD) (TpCum,MeZn+ = zinc(II) hydro-tris(3-cumenyl-5-methylpyrazolyl)borate complex cation; SQ = orthosemiquinone; VD = oxoverdazyl), which is a ground-state analogue of a charge-separated excited state, has been synthesized and structurally characterized. The magnetic exchange interaction between the S = 1/2 SQ and the S = 1/2 VD within the SQ-VD biradical ligand is observed to be ferromagnetic, with JSQ-VD = +77 cm-1 (H = -2JSQ-VDŜSQ·ŜVD) determined from an analysis of the variable-temperature magnetic susceptibility data. The pairwise biradical exchange interaction in TpCum,MeZn(SQ-VD) can be compared with that of the related donor-acceptor biradical complex TpCum,MeZn(SQ-NN) (NN = nitronyl nitroxide, S = 1/2), where JSQ-NN ≅ +550 cm-1. This represents a dramatic reduction in the biradical exchange by a factor of ∼7, despite the isolobal nature of the VD and NN acceptor radical SOMOs. Computations assessing the magnitude of the exchange were performed using a broken-symmetry density functional theory (DFT) approach. These computations are in good agreement with those computed at the CASSCF NEVPT2 level, which also reveals an S = 1 triplet ground state as observed in the magnetic susceptibility measurements. A combination of electronic absorption spectroscopy and CASSCF computations has been used to elucidate the electronic origin of the large difference in the magnitude of the biradical exchange coupling between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN). A Valence Bond Configuration Interaction (VBCI) model was previously employed to highlight the importance of mixing an SQSOMO → NNLUMO charge transfer configuration into the electronic ground state to facilitate the stabilization of the high-spin triplet (S = 1) ground state in TpCum,MeZn(SQ-NN). Here, CASSCF computations confirm the importance of mixing the pendant radical (e.g., VD, NN) LUMO (VDLUMO and NNLUMO) with the SOMO of the SQ radical (SQSOMO) for stabilizing the triplet, in addition to spin polarization and charge transfer contributions to the exchange. An important electronic structure difference between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN), which leads to their different exchange couplings, is the reduced admixture of excited states that promote ferromagnetic exchange into the TpCum,MeZn(SQ-VD) ground state, and the intrinsically weaker mixing between the VDLUMO and the SQSOMO compared to that observed for TpCum,MeZn(SQ-NN), where this orbital mixing is significant. The results of this comparative study contribute to a greater understanding of biradical exchange interactions, which are important to our understanding of excited-state singlet-triplet energy gaps, electron delocalization, and the generation of electron spin polarization in both the ground and excited states of (bpy)Pt(CAT-radical) complexes.

Power Decoupling Strategy for Voltage Modulated Direct Power Control of Voltage Source Inverters Connected to Weak Grids

The grid voltage modulated direct power control (GVM-DPC)-based inverter is an attractive solution to regulate the instantaneous real and reactive powers injected into power grids. However, the power coupling in GVM-DPC, i.e., interactions between the real and reactive power loops, may deteriorate its transient performance. In this paper, a power decoupling strategy for GVM-DPC is proposed based on a dynamic feedforward power compensation (DFPC) algorithm. It is proved that the proposed strategy has better decoupling performance than that of the traditional virtual impedance method (VIM). Firstly, power coupling characteristics in GVM-DPC are analyzed, indicating that the ignorance of voltage angle variation at the point of common coupling (PCC) will result in severe power coupling. Then, power coupling magnitudes are derived according to relationships among the real power, reactive power and PCC voltage. Next, the coupling magnitudes are compensated into the power control loop of the GVM-DPC for the better decoupling performance. The transient performance of inverter using DFPC is studied based on the impedance analysis. Also, the relationship between coupling magnitude and grid side impedance is studied, which indicates the limited power decoupling capability of VIM. Finally, the proposed method is validated by the simulations and a hardware-in-loop system.

Correlation between the magnitude of interlayer exchange coupling and charge-to-spin conversion efficiency in a synthetic antiferromagnetic system

The correlation between the magnitude of interlayer exchange coupling (J ex) and charge-to-spin conversion efficiency (spin Hall angle: θ SH) is investigated in a synthetic antiferromagnetic (AF) system with compensated magnetization. The magnitude of θ SH increases linearly with increasing the magnitude of J ex. We observe the factor of 6.5 increase of spin Hall angle (θ SH = 45.8%) in a low resistive (ρ xx = 41 μΩcm) synthetic AF system by increasing the magnitude of J ex. The low resistive synthetic AF system will be a promising building block for future nonvolatile high-speed memories and logic circuits using the spin Hall effect.

Collective Dynamical Behaviors of Nonlocally Coupled Brockett Oscillators

In this study, we consider a network of nonlocally coupled Brockett oscillators (BOs) with attractive and repulsive (AR) couplings to illustrate the existence of diverse collective dynamical behaviors, whereas previous studies solely concentrated on synchronization. In the absence of coupling, the individual BO oscillator shows stable periodic oscillations (POs) or stable steady state (SS) depending on the critical values of the parameters. We first begin by examining the collective dynamics by setting the critical value of the parameters at the active (PO) region. A diverge collective dynamical states are manifested for a fixed nonlocal coupling range with rising coupling magnitude. Notably, the lower coupling strength exhibits two distinct dynamical patterns at lower and higher transients. At lesser transients, for example, transient dynamics of desynchronization, chimera, and traveling wave states are observed. At larger time periods, the transient dynamics disappear with the emergence of a synchronized state. Increasing the coupling strength results in a unique state of traveling wave or synchronized state for smaller and larger time periods depending on the coupling strength. Increasing the coupling strength further gives rise to clustering behaviors. Importantly, the considered system attains cluster oscillation death (COD) through a cluster oscillatory state (COS). Finally, there exists a chimera death at a larger coupling strength. The observed dynamical transitions are further demonstrated through the two‐parameter analysis by setting different critical thresholds.

Computational Exploration of the Intersystem Crossing from the X̃3A2 to the ã1A1 State in Boryl Nitrenes upon Photoexcitation.

The boryl nitrene CatBN (Cat = catecholato) turns highly reactive toward small inert molecules upon irradiation of its triplet ground state X̃3A2 with light of wavelength λ > 550 nm. A computational study of a model boryl nitrene using complete active space self-consistent field (CASSCF) theory provides evidence for the population of the highly reactive electronic state ã1A1 upon irradiation. Potential energy scans connecting different critical points (minima, minimum energy crossing points, and conical intersections) reveal two possible pathways that could relax photoexcited boryl nitrene from the Franck-Condon region of Ã3B1 to the ã1A1 state minimum. Considering the energy barriers to relaxation from one electronic state to another and the magnitude of spin-orbit couplings, the energetically most favorable pathway involves photoexcitation to Ã3B2, followed by intersystem crossing to the open-shell singlet state (b̃1A2) and internal conversion to ã1A1. The relevant minimum energy crossing point is about 7-8 kcal mol-1 higher in energy than the Franck-Condon region.

Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence.

In order to investigate the joint influence of the conformation flexibility and the matching of the energies of the charge-transfer (CT) and the localized triplet excited (3LE) states on the thermally activated delayed fluorescence (TADF) in electron donor–acceptor molecules, a series of compact electron donor–acceptor dyads and a triad were prepared, with naphthalimide (NI) as electron acceptor and phenothiazine (PTZ) as electron donor. The NI and PTZ moieties are either directly connected at the 3-position of NI and the N-position of the PTZ moiety via a C–N single bond, or they are linked through a phenyl group. The tuning of the energy order of the CT and LE states is achieved by oxidation of the PTZ unit into the corresponding sulfoxide, whereas conformation restriction is imposed by introducing ortho-methyl substituents on the phenyl linker, so that the coupling magnitude between the CT and the 3LE states can be controlled. The singlet oxygen quantum yield (ΦΔ) of NI-PTZ is moderate in n-hexane (HEX, ΦΔ = 19%). TADF was observed for the dyads, the biexponential luminescence lifetime are 16.0 ns (99.9%)/14.4 μs (0.1%) for the dyad and 7.2 ns (99.6%)/2.0 μs (0.4%) for the triad. Triplet state was observed in the nanosecond transient absorption spectra with lifetimes in the 4–48 μs range. Computational investigations show that the orthogonal electron donor–acceptor molecular structure is beneficial for TADF. These calculations indicate small energetic difference between the 3LE and 3CT states, which are helpful for interpreting the ns-TA spectra and the origins of TADF in NI-PTZ, which is ultimately due to the small energetic difference between the 3LE and 3CT states. Conversely, NI-PTZ-O, which has a higher CT state and bears a much more stabilized 3LE state, does not show TADF.

Deep learning-assisted multifunctional wavefront modulation with Willis coupling

Diverse wavefront modulations with multifunctional acoustic devices have been of great interest to physics and engineering communities. However, traditional design methods of multifunctional acoustic devices rely on a deterministic physical model and redundant iterative optimization, resulting in inflexibility and consuming of time. In this work, we present and experimentally implement a deep learning-assisted tunable acoustic metagrating for multifunctional wavefront modulation with 95.2% accuracy and a 105 order of magnitude decrease in computational time compared to a classical optimization method. The presented tunable structure formed by a periodic array of 3C-shaped unit cells excites controllable Willis coupling, exhibiting corresponding asymmetrical scattering patterns. With the support of a deep learning strategy, the optimal configuration between structure parameters and Willis coupling magnitude could be efficiently confirmed, realizing various extraordinary wavefront modulations, including abnormal reflection, perfect beam splitting, and multi-channel energy distribution in arbitrary ratios. The polarizability tensor retrieval method is used to characterize the Willis coupling of different modulation structures, demonstrating the refined abstraction of the deep learning strategy on Willis coupling. Meanwhile, the numerical and experimental results are in good agreement with the desired wavefront modulation, verifying the effectiveness of the proposed method. Our work develops deep learning-assisted multifunctional wavefront modulation with the advantages of high accuracy, efficiency, flexibility, and refined abstraction of a physical mechanism, paving the way for a combination of deep learning and pragmatic multifunctional acoustic applications.

First Indirect Detection Constraints on Axions in the Solar Basin.

Axions with masses of order keV can be produced in great abundance within the Solar core. The majority of Sun-produced axions escape to infinity, but a small fraction of the flux is produced with speeds below the escape velocity. Over time, this process populates a basin of slow-moving axions trapped on bound orbits. These axions can decay to two photons, yielding an observable signature. We place the first limits on this solar basin of axions using recent quiescent solar observations made by the NuSTAR x-ray telescope. We compare three different methodologies for setting constraints, and obtain world-leading limits for axions with masses between 5 and 30keV, in some cases improving on stellar cooling bounds by more than an order of magnitude in coupling.

Analytical interpretation and numerical simulation on the dynamic coupling of a flexible cyclic blades-disk-shaft system

This paper focuses on the influence mechanism of cyclic blades on the dynamic coupling of a flexible shaft-disk-blade (FSDB) system through mathematical analysis and numerical simulation. Firstly, a coupling mechanism model of an FSDB unit is developed through a Lagrange method and the assumed mode method (AMM), after considering the coupling behavior among shaft bending, shaft torsion, disk vibration, and blade bending. The modal comparison results between the proposed model and FEM affirm the validity of the model. Then the analytical interpretation is explored by decomposing and discussing the diagonal coupling and cross-coupling matrices of the FSDB system. The mechanism discussion reveals that the coupling matrices originate from the rigid and elastic motions of flexible disk and cyclic blades, indicating that the motions of cyclic blades play an important role in dynamic coupling. Therefore, the motions of cyclic blades are classified and analyzed, and their effects on natural frequencies (NFs) and critical speeds (CSs) are applied to further interpret and validate the dynamic coupling through numerical simulation. The numerical results indicate that motions of cyclic blades can increase, decrease, and eliminate the magnitude of dynamic coupling significantly.

Proximity effects in graphene on monolayers of transition-metal phosphorus trichalcogenides MPX3 (M:Mn, Fe, Ni, Co, and X: S, Se)

We investigate the electronic band structure of graphene on a series of two-dimensional magnetic transition-metal phosphorus trichalcogenide monolayers, ${M\text{P}X}_{3}$ with $M={\mathrm{Mn},\mathrm{Fe},\mathrm{Ni},\mathrm{Co}}$ and $X={\mathrm{S},\mathrm{Se}}$, with first-principles calculations. A symmetry-based model Hamiltonian is employed to extract orbital parameters and sublattice resolved proximity-induced exchange couplings (${\ensuremath{\lambda}}_{\text{ex}}^{\text{A}}$ and ${\ensuremath{\lambda}}_{\text{ex}}^{\text{B}}$) from the low-energy Dirac bands of the proximitized graphene. Depending on the magnetic phase of the ${M\text{P}X}_{3}$ layer (ferromagnetic and three antiferromagnetic ones), completely different Dirac dispersions can be realized with exchange splittings ranging from 0 to 10 meV. Remarkably, not only the magnitude of the exchange couplings depends on the magnetic phase, but also the global sign and the type. Important, one can realize uniform $({\ensuremath{\lambda}}_{\text{ex}}^{\text{A}}\ensuremath{\approx}{\ensuremath{\lambda}}_{\text{ex}}^{\text{B}})$ and staggered $({\ensuremath{\lambda}}_{\text{ex}}^{\text{A}}\ensuremath{\approx}\ensuremath{-}{\ensuremath{\lambda}}_{\text{ex}}^{\text{B}})$ exchange couplings in graphene. From selected cases we find that the interlayer distance, as well as a transverse electric field, are efficient tuning knobs for the exchange splittings of the Dirac bands. More specifically, decreasing the interlayer distance by only about 10%, a giant fivefold enhancement of proximity exchange is found, while applying few V/nm of electric field, provides tunability of proximity exchange by tens of percent. We have also studied the dependence on the Hubbard $U$ parameter and find it to be weak. Moreover, we find that the effect of SOC on the proximitized Dirac dispersion is negligible compared to the exchange coupling.

A nonlinear memductance induced intermittent and anti-phase synchronization.

We introduce a model to mimic the dynamics of oscillators that are coupled by mean-field nonlinear memductance. Notably, nonlinear memductance produces dynamic nonlinearity, which causes the direction of coupling to change over time. Depending on the parameters, such a dynamic coupling drives the trajectory of oscillators to a synchronization or anti-synchronization manifold. Specifically, depending on the forcing frequency and coupling strength, we find anti-phase and intermittent synchronization. With the increase in coupling magnitude, one can observe a transition from intermittent synchronization to complete synchronization through anti-phase synchronization. The results are validated through numerical simulations. The hypothesis has a huge impact on the study of neuronal networks.

Naphthalimide-Carbazole Compact Electron Donor-Acceptor Dyads: Effect of Molecular Geometry and Electron-Donating Capacity on the Spin-Orbit Charge Transfer Intersystem Crossing.

We prepared a series of naphthalimide (NI)-carbazole (Cz) compact electron donor-acceptor dyads showing different substitution positions, C-N/C-C linkers, and conformation restriction magnitudes to study the spin-orbit charge transfer intersystem crossing (SOCT-ISC). The varied conformation restrictions lead to different dihedral angles between the donor and acceptor (37°-81°) and electronic coupling magnitude (matrix elements V: 1290-3070 cm-1). Based on the comparison between the dyads containing C-N and C-C linkers, we found that a large dihedral angle between the donor and acceptor is favorable to efficient SOCT-ISC. For one dyad, the singlet oxygen quantum yield (ΦΔ) is up to 84.4% (in dichloromethane), which is much higher than that of the previously reported NI-phenothiazine (PTZ) analogue dyad (ΦΔ = 16.0% in n-hexane). The intrinsic triplet state lifetime (τT) is 270 μs, longer than that accessed by the heavy atom effect (75.2 μs). As compared with the NI-PTZ analogue dyad, the Cz unit in the current dyads is a weaker electron donor than PTZ. Thus, a higher CT state energy in NI-Cz dyads was observed, which makes the SOCT-ISC efficient in solvents with a wide range of polarities. Meanwhile, the localized triplet state (3LE) becomes the lowest-lying state in the NI-Cz dyads, which is different from the triplet charge transfer (3CT) state observed in the analogue NI-PTZ dyad. Moreover, the large energy gap between the CT and 3LE states inhibits the reverse ISC; as a result, no thermally activated delayed fluorescence was observed for the current NI-Cz dyads.

Enhancement of charging performance of quantum battery via quantum coherence of bath

An open quantum battery (QB) model of a single qubit system charging in a coherent auxiliary bath (CAB) consisting of a series of independent coherent ancillae is considered. According to the collision charging protocol we derive a quantum master equation and obtain the analytical solution of QB in a steady state. We find that the full charging capacity (or the maximal extractable work (MEW)) of QB, in the weak QB-ancilla coupling limit, is positively correlated with the coherence magnitude of ancilla. Combining with the numerical simulations we compare with the charging properties of QB at finite coupling strength, such as the MEW, average charging power and the charging efficiency, when considering the bath to be a thermal auxiliary bath (TAB) and a CAB, respectively. We find that when the QB with CAB, in the weak coupling regime, is in fully charging, both its capacity and charging efficiency can go beyond its classical counterpart, and they increase with the increase of coherence magnitude of ancilla. In addition, the MEW of QB in the regime of relative strong coupling and strong coherent magnitude shows the oscillatory behavior with the charging time increasing, and the first peak value can even be larger than the full charging MEW of QB. This also leads to a much larger average charging power than that of QB with TAB in a short-time charging process. These features suggest that with the help of quantum coherence of CAB it becomes feasible to switch the charging schemes between the long-time slow charging protocol with large capacity and high efficiency and the short-time rapid charging protocol with highly charging power only by adjusting the coupling strength of QB-ancilla. This work clearly demonstrates that the quantum coherence of bath can not only serve as the role of “fuel” of QB to be utilized to improve the QB’s charging performance but also provide an alternative way to integrate the different charging protocols into a single QB.

On The Biophysical Complexity of Brain Dynamics: An Outlook

The human brain is a complex network whose ensemble time evolution is directed by the cumulative interactions of its cellular components, such as neurons and glia cells. Coupled through chemical neurotransmission and receptor activation, these individuals interact with one another to varying degrees by triggering a variety of cellular activity from internal biological reconfigurations to external interactions with other network agents. Consequently, such local dynamic connections mediating the magnitude and direction of influence cells have on one another are highly nonlinear and facilitate, respectively, nonlinear and potentially chaotic multicellular higher-order collaborations. Thus, as a statistical physical system, the nonlinear culmination of local interactions produces complex global emergent network behaviors, enabling the highly dynamical, adaptive, and efficient response of a macroscopic brain network. Microstate reconfigurations are typically facilitated through synaptic and structural plasticity mechanisms that alter the degree of coupling (magnitude of influence) neurons have upon each other, dictating the type of coordinated macrostate emergence in populations of neural cells. These can emerge in the form of local regions of synchronized clusters about a center frequency composed of individual neural cell collaborations as a fundamental form of collective organization. A single mode of synchronization is insufficient for the computational needs of the brain. Thus, as neural components influence one another (cellular components, multiple clusters of synchronous populations, brain nuclei, and even brain regions), different patterns of neural behavior interact with one another to produce an emergent spatiotemporal spectral bandwidth of neural activity corresponding to the dynamical state of the brain network. Furthermore, hierarchical and self-similar structures support these network properties to operate effectively and efficiently. Neuroscience has come a long way since its inception; however, a comprehensive and intuitive understanding of how the brain works is still amiss. It is becoming evident that any singular perspective upon the grandiose biophysical complexity within the brain is inadequate. It is the purpose of this paper to provide an outlook through a multitude of perspectives, including the fundamental biological mechanisms and how these operate within the physical constraints of nature. Upon assessing the state of prior research efforts, in this paper, we identify the path future research effort should pursue to inspire progress in neuroscience.

Local structure-function relationships in human brain networks across the lifespan

A growing number of studies have used stylized network models of communication to predict brain function from structure. Most have focused on a small set of models applied globally. Here, we compare a large number of models at both global and regional levels. We find that globally most predictors perform poorly. At the regional level, performance improves but heterogeneously, both in terms of variance explained and the optimal model. Next, we expose synergies among predictors by using pairs to jointly predict FC. Finally, we assess age-related differences in global and regional coupling across the human lifespan. We find global decreases in the magnitude of structure-function coupling with age. We find that these decreases are driven by reduced coupling in sensorimotor regions, while higher-order cognitive systems preserve local coupling with age. Our results describe patterns of structure-function coupling across the cortex and how this may change with age.

Magnon mode transition in synthetic antiferromagnets induced by perpendicular magnetic anisotropy

In this work, we numerically studied the static and dynamic properties of synthetic antiferromagnets (SAFs) with perpendicular magnetic anisotropy (PMA). The observed high/low frequency magnon is either optical/acoustic or left/right-hand mode depending on the strength of PMA, i.e., a PMA-induced magnon mode transition. For weaker PMA, the ground magnetization state of the SAFs is in-plane magnetized exhibiting the optical/acoustic magnon mode with high/low frequency. While for stronger PMA, the ground magnetization state of the SAFs is perpendicularly magnetized and characterized by the presence of the left- and right-hand magnon modes. Furthermore, by tilting the external field toward the SAF film plane, hybridization between the acoustic and the optical magnon modes can be realized and approaches a strong coupling regime by modulating the strength of PMA and the magnitude of interlayer exchange coupling. Our findings provide new insight into the magnetization dynamics in synthetic antiferromagnets with perpendicular magnetic anisotropy for quantum magnonics.

Negative Newton constant may destroy some conjectures

The magnitude and sign of the gravitational coupling [Formula: see text] depend on the relations between different contributions from scalar, fermionic and vector fields. In principle, this may give the zero and negative values of [Formula: see text] in some hypothetical Universes with the proper relations between the fermionic and bosonic species. We consider different conjectures related to gravity, such as the wave function collapse caused by gravity, entropic gravity and maximum force. We find that some of them do not work in the Universes with zero or negative [Formula: see text], and thus cannot be considered as universal. Thus, the extension of the gravitational coupling to [Formula: see text] provides the test on the universality of the proposed theories of gravity.

BICEP/ Keck constraints on attractor models of inflation and reheating

Recent BICEP/Keck data on the cosmic microwave background, in combination with previous WMAP and Planck data, impose strong new constraints on the tilt in the scalar perturbation spectrum, ${n}_{s}$, as well as the tensor-to-scalar ratio, $r$. These constrain the number of $e$-folds of inflation, ${N}_{*}$, the magnitude of the inflaton coupling to matter, $y$, and the reheating temperature, ${T}_{\mathrm{reh}}$, which we evaluate in attractor models of inflation as formulated in no-scale supergravity. The 68% C.L. region of $({n}_{s},r)$ favors large values of ${N}_{*},y$, and ${T}_{\mathrm{reh}}$ that are constrained by the production of gravitinos and supersymmetric dark matter.

Geometry Dependence of Spin-Orbit Coupling in Complexes of Molecular Oxygen with Atoms, H2, or Organic Molecules.

Studies of the interactions between molecular oxygen and a perturbing species, such as an organic solvent, have been an active research area for at least 70 years. In particular, interaction with a neighboring molecule or atom may perturb the electronic states of oxygen to such an extent that the O2(a1Δg) → O2(X3Σg-) transition, formally forbidden as an electric dipole process, achieves significant transition probability. We present a computational study of how the geometry of complexes consisting of molecular oxygen and different perturbing species influences the magnitude of spin-orbit coupling that facilitates the O2(a1Δg) → O2(X3Σg-) transition. We rationalize our results using a model based on orbital interactions: a non-zero spin-orbit coupling matrix element results from asymmetric transfer of charge to or from the 1πg orbitals on oxygen. Our results indicate that the atoms in a perturbing species closest to oxygen are responsible for the majority of the spin-orbit interactions, suggesting that large systems can be simplified appreciably. Furthermore, we infer and confirm that an estimate of the spin-orbit coupling matrix element can be obtained from the magnitude of the induced energy splitting of oxygen's 1πg orbitals. These results should provide further momentum in the long-standing issue of understanding phenomena that influence the O2(a1Δg) → O2(X3Σg-) transition.