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Université de Fribourg

On exchange coupling and bonding in the Gd2@C80 and Gd2@C79N endohedral dimetallo-fullerenes

Cimpoesu, Fanica ; Frecus, Bogdan ; Oprea, Corneliu I. ; Ramanantoanina, Harry ; Urland, Werner ; Daul, Claude

In: Molecular Physics, 2015, vol. 113, no. 13-14, p. 1712–1727

A series of computational experiments performed with various methods belonging to wave-function and density functional theories approaches the issue of bonding regime and exchange coupling in the title compounds. Gd₂@C₈₀ is computed with a very weak exchange coupling, the sign depending on the method, while Gd₂@C₇₉N has resulted with a strong coupling and ferromagnetic ground state,...

Université de Fribourg

The theoretical account of the ligand field bonding regime and magnetic anisotropy in the DySc₂N@C₈₀ single ion magnet endohedral fullerene

Cimpoesu, Fanica ; Dragoe, Nita ; Ramanantoanina, Harry ; Urland, Werner ; Daul, Claude

In: Physical Chemistry Chemical Physics, 2014, vol. 16, no. 23, p. 11337–11348

Considering the DySc₂N@C₈₀ system as a prototype for Single Ion Magnets (SIMs) based on endohedral fullerenes, we present methodological advances and state-of-the art computations analysing the electronic structure and its relationship with the magnetic properties due to the Dy(III) ion. The results of the quantum chemical calculations are quantitatively decrypted in the framework of ligand...

Université de Fribourg

A ligand field theory-based methodology for the characterization of the Eu²⁺ [Xe]4f⁶5d¹ excited states in solid state compounds

García-Fuente, Amador ; Cimpoesu, Fanica ; Ramanantoanina, Harry ; Herden, Benjamin ; Daul, Claude ; Suta, Markus ; Wickleder, Claudia ; Urland, Werner

In: Chemical Physics Letters, 2015, vol. 622, p. 120–123

The theoretical rationalization of the open-shell 4f and 5d configuration of Eu²⁺ is by far not trivial because it involves a non-standard version of ligand field theory, based on a two-shell Hamiltonian. Here we present our methodology based on ligand field theory, taking the system CsCaBr₃:Eu²⁺ as a case study with an octahedral coordination sphere of Eu²⁺. The ligand field,...

Université de Fribourg

Photon cascade emission in Pr³⁺ doped fluorides with CaF₂ structure: Application of a model for its prediction

Herden, Benjamin ; García-Fuente, Amador ; Ramanantoanina, Harry ; Jüstel, Thomas ; Daul, Claude ; Urland, Werner

In: Chemical Physics Letters, 2015, vol. 620, p. 29–34

In this work, we predict and measure the optical behaviour of Pr³⁺ in different binary and ternary fluorides. We use a validated model based on Ligand Field Theory and Density Functional Theory to calculate the multiplet energy levels arising from the ground [Xe]4f² and excited [Xe]4f¹5d¹ electron configurations of Pr³⁺ in its chemical environment. Moreover, the luminescence spectra of...

Université de Fribourg

Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study of Uranium(IV)-Containing A₂USi₆O₁₅ (A = K, Rb) with an Intriguing Green-to-Purple, Crystal-to-Crystal Structural Transition in the K Analogue

Morrison, Gregory ; Ramanantoanina, Harry ; Urland, Werner ; Smith, Mark D. ; Loye, Hans-Conrad zur

In: Inorganic Chemistry, 2015, vol. 54, no. 11, p. 5504–5511

Single crystals of uranium(IV)-containing A₂USi₆O₁₅ (A = K, Rb) were grown using the flux growth method. The two compounds crystallize in a new structure type related to Cs₂USi₆O₁₅. K₂USi₆O₁₅ exhibits an interesting crystal-to-crystal transition, which is accompanied by an intense color change. Magnetic properties are reported for A₂USi₆O₁₅ and differ from other...

Université de Fribourg

Jahn–Teller instability in cationic boron and carbon buckyballs B₈₀⁺ and C₆₀⁺: a comparative study

Muya, Jules Tshishimbi ; Ramanantoanina, Harry ; Daul, Claude A. ; Nguyen, Minh Tho ; Gopakumar, G. ; Ceulemans, Arnout

In: Physical Chemistry Chemical Physics, 2013, vol. 15, no. 8, p. 2829-2835

This paper investigates the Jahn–Teller effect in the icosahedral cation B₈₀⁺ and compares the descent in symmetry with that in C₆₀⁺. For both cations the icosahedral ground state is a ²Hu state, which exhibits a H ⊗ (g ⊕ 2h) Jahn–Teller instability. A detailed construction of the potential energy surface of B₈₀⁺ using different DFT methods including...

Université de Fribourg

Ligand field density functional theory calculation of the 4f² → 4f¹5d¹ transitions in the quantum cutter Cs₂KYF₆:Pr³⁺

Ramanantoanina, Harry ; Urland, Werner ; Cimpoesu, Fanica ; Daul, Claude

In: Physical Chemistry Chemical Physics, 2013, vol. 15, no. 33, p. 13902–13910

Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4fⁿ → 4fⁿ⁻¹5d¹ transitions in rare earth compounds and apply it for the characterization of the 4f² → 4f¹5d¹ transitions in the quantum cutter Cs₂KYF₆:Pr³⁺ with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of...

Université de Fribourg

Development and applications of the LFDFT: the non-empirical account of ligand field and the simulation of the f–d transitions by density functional theory

Ramanantoanina, Harry ; Sahnoun, Mohammed ; Barbiero, Andrea ; Ferbinteanu, Marilena ; Cimpoesu, Fanica

In: Physical Chemistry Chemical Physics, 2015, vol. 17, no. 28, p. 18547–18557

Ligand field density functional theory (LFDFT) is a methodology consisting of non-standard handling of DFT calculations and post-computation analysis, emulating the ligand field parameters in a non-empirical way. Recently, the procedure was extended for two-open-shell systems, with relevance for inter-shell transitions in lanthanides, of utmost importance in understanding the optical and magnetic...

Université de Fribourg

General treatment of the multimode Jahn–Teller effect: study of fullerene cations

Ramanantoanina, Harry ; Zlatar, Matija ; García-Fernández, Pablo ; Daul, Claude A. ; Gruden-Pavlović, Maja

In: Physical Chemistry Chemical Physics, 2013, vol. 15, no. 4, p. 1252-1259

A general model for the analysis of the Adiabatic Potential Energy Surfaces (APES) of the molecules that are subject to the multimode Jahn–Teller effect is presented. The method utilizes the information obtained by DFT calculations on a distorted stationary point on the APES. The essence of the model is to express the distortion along a model minimal energy path called Intrinsic Distortion Path...

Université de Fribourg

The angular overlap model extended for two-open-shell f and d electrons

Ramanantoanina, Harry ; Urland, Werner ; Cimpoesu, Fanica ; Daul, Claude

In: Physical Chemistry Chemical Physics, 2014, vol. 16, no. 24, p. 12282–12290

We discuss the applicability of the Angular Overlap Model (AOM) to evaluate the electronic structure of lanthanide compounds, which are currently the subject of incredible interest in the field of luminescent materials. The functioning of phosphors is well established by the f–d transitions, which requires the investigation of both the ground 4fn and excited 4fn−15d1 electron configurations...