Adiabatic and nonadiabatic static polarizabilities of H and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

Tiihonen, Juha; Kylänpää, Ilkka; Rantala, Tapio T.

doi:10.1103/physreva.91.062503

Cited by 9 publications

(14 citation statements)

References 23 publications

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“…Difficulties in constructing reasonable wave function ansatz in the case of the larger complexes hinders straightforward extension of the simple variational models. Within the effective mass approach, quantum Monte Carlo (QMC) methods, such as diffusion Monte Carlo and path integral Monte Carlo (PIMC), provide accurate and powerful means for studying few-particle systems [17][18][19] . The main advantage in QMC methods is the exact account of particle-particle correlations, which is particularly important in accurate description of exciton complexes.…”

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confidence: 99%

Binding energies of exciton complexes in transition metal dichalcogenide monolayers and effect of dielectric environment

2015

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Excitons, trions, biexcitons, and exciton-trion complexes in two-dimensional transition metal dichalcogenide sheets of MoS2, MoSe2, MoTe2, WS2 and WSe2 are studied by means of density functional theory and path integral Monte Carlo method in order to accurately account for the particle-particle correlations. In addition, the effect of dielectric environment on the properties of these exciton complexes is studied by modifying the effective interaction potential between particles. Calculated exciton and trion binding energies are consistent with previous experimental and computational studies, and larger systems such as biexciton and exciton-trion complex are found highly stable. Binding energies of biexcitons are similar or higher than those of trions, but the binding energy of the trion depends significantly stronger on the dielectric environment than that of biexciton. Therefore, as a function of an increasing dielectric constant of the environment the exciton-trion complex "dissociates" to a biexciton rather than to an exciton and a trion.Layered transition metal dichalcogenides (TMD) are chemically, thermally, and mechanically stable even in the monolayer form, and thus, provide an ideal platform for studying condensed matter physics in two dimensions. The semiconducting TMDs present many unusual optical properties such as strong excitonic effects 1 , valley-dependent circular dichroism 2 , and second-harmonic generation 3 , whose magnitude depends sensitively on the number of layers. For instance, the prototypical MoS 2 material is a semiconductor with 1.1 eV indirect band gap in bulk, but 1.9 eV direct band gap in the monolayer 1 . Importantly, the reduced dimensionality is manifested in a large exciton binding energy of 0.5-1 eV, but also of significant binding energy in the case of charged excitons, or trions, consisting of three charge carriers. This suggests that even larger complexes might be stable. Indeed, first experimental reports assigned to biexciton formation have very recently appeared in the literature [4][5][6] . Theoretical studies are invaluable in predicting the stability of these complexes and in interpreting the experimental results. Excitons can be calculated reliably from firstprinciples by solving the Bethe-Salpeter equation (BSE) on top of quasi-particle band structure. Binding energies have also been calculated using simple variational or tight-binding models based on an effective 2D interaction potential and the effective mass approach 6-13 , yielding fairly good agreement with experiments and with the BSE results in the case of excitons. This has also raised interest to apply similar approaches to study larger exciton complexes 6,14 , in comparison to the theoretical estimates based on quantum well systems 4,15,16 . Difficulties in constructing reasonable wave function ansatz in the case of the larger complexes hinders straightforward extension of the simple variational models. Within the effective mass approach, quantum Monte Carlo (QMC) methods, such as diffusion Monte Carlo and...

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Binding energies of exciton complexes in transition metal dichalcogenide monolayers and effect of dielectric environment

2015

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“…In our recent article [5], we proposed a scheme for estimating static dipole polarizabilities in a field-free PIMC simulation. This was an imminent improvement to our earlier finite-field approach [6]. The resulting properties, including substantial rovibrational effects, were those corresponding to an isolated molecule in low density gas.…”

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confidence: 73%

“…[1]. In Table I, we present BO results for all of the spherically symmetric systems: B zz,zz , C zz,zz and the total energy E. Furthermore, the results for the molec- (7) and for HeH + A z,zz = −0.48 (6) and A x,zx = −0.0657 (10). The principal axis z is by default the line connecting the two nuclei, but for triangular H + 3 it is perpendicular to the plane of protons.…”

Section: Resultsmentioning

confidence: 99%

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Static field-gradient polarizabilities of small atoms and molecules at finite temperature

Tiihonen

Kylänpää

Rantala

2017

The Journal of Chemical Physics

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In this work, we propose new field-free estimators for static field-gradient polarizabilities in finite temperature PIMC simulation. Namely, dipole-quadrupole polarizability A, dipole-dipolequadrupole polarizability B and quadrupole-quadrupole polarizability C are computed for several up to two-electron systems: H, H − , He, Li + , Be 2+ , Ps2, PsH, H + 2 , H2, H + 3 and HeH + . We provide complementary data for ground state electronic properties within the adiabatic approximation, and demonstrate good agreement with available values in the literature. More importantly, we present fully non-adiabatic results from 50 K to 1600 K, which allow us to analyze and discuss strong thermal coupling and rovibrational effects in total field-gradient polarizabilities. These phenomena are most relevant but clearly overlooked, e.g., in the construction of modern polarizable force field models. However, our main purpose is demonstrating the accuracy and simplicity of our approach in a problem that is generally challenging.

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“…In recent years, one of the authors of this tutorial (TTR) has significantly contributed to taking PIMC simulations to new though simple quantum particle systems, such as small atoms 60,61 , molecules [62][63][64][65] , a chemical reaction 66 and quantum dots [67][68][69] , with the ultimate goal of providing a more accurate description of their electronic structure and related properties including many-body effects, and how they change with temperature 61,70,71 . In this context, PIMC has proven to be a very reliable and excellent method to calculate the electric polarisabilities of atomic and molecular systems, leading therefore to an accurate estimation of the optical properties of both individual small quantum systems and collections of them, in the form of dilute gases 65,72,73 .…”

Section: Introductionmentioning

confidence: 99%

Path Integrals: From Quantum Mechanics to Photonics

Robson¹,

Tamashevich²,

Rantala³

et al. 2021

Preprint

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The path integral formulation of quantum mechanics, i.e., the idea that the evolution of a quantum system is determined as a sum over all the possible trajectories that would take that system from the initial to the final state of its dynamical evolution, is perhaps the most elegant and universal framework developed in theoretical physics, second only to the Standard Model of particle physics. In this tutorial, we retrace the steps that led to the creation of such a remarkable framework, discuss its foundations, and present some of the classical examples of problems that can be solved using the path integral formalism, as a way to introduce the readers to the topic, and help them get familiar with the formalism. Then, we focus our attention on the use of path integrals in optics and photonics, and discuss in detail how they have been used in the past to approach several problems, ranging from the propagation of light in inhomogeneous media, to parametric amplification, and quantum nonlinear optics in arbitrary media. To complement this, we also briefly present the Path Integral Monte Carlo (PIMC) method, as a valuable computational resource for condensed matter physics, and discuss its potential applications and advantages if used in photonics.

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Adiabatic and nonadiabatic static polarizabilities of H andH2

Cited by 9 publications

References 23 publications

Binding energies of exciton complexes in transition metal dichalcogenide monolayers and effect of dielectric environment

Binding energies of exciton complexes in transition metal dichalcogenide monolayers and effect of dielectric environment

Static field-gradient polarizabilities of small atoms and molecules at finite temperature

Path Integrals: From Quantum Mechanics to Photonics

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