Hybrid organic-inorganic CH3NH3MnS3 : a multifunctional material for energy conversion, radiation protection, and hydrogen storage.

CONTEXT: Hybrid organic-inorganic chalcogenides have emerged as promising multifunctional materials due to their structural flexibility and tunable physical properties, making them attractive candidates for energy-conversion, optoelectronic, environmental, and radiation-protection technologies. In this study, the structural, electronic, mechanical, optical, thermodynamic, radiation-shielding, and hydrogen-storage properties of CH3NH3MnS3 were comprehensively investigated. The optimized structure exhibits excellent stability, while mechanical analysis confirms elastic stability and anisotropic behavior. Optical calculations reveal strong absorption across the visible and ultraviolet regions, accompanied by a high dielectric response, moderate refractive index, and low reflectivity, indicating suitability for photovoltaic and photodetection applications. Dynamical and thermal stability are verified through phonon-dispersion and thermodynamic analyses. Radiation-shielding calculations demonstrate efficient attenuation of low-energy photons with small half-value and tenth-value layers. Furthermore, hydrogen-storage investigations predict favorable adsorption energetics, a gravimetric storage capacity of approximately 13.2 wt.%, and a low diffusion barrier of about 0.32 eV, facilitating rapid hydrogen transport. These findings identify CH3NH3MnS3 as a versatile multifunctional material with significant potential for next-generation energy, optoelectronic, hydrogen-storage, and radiation-shielding applications. METHODS: The structural, electronic, optical, elastic, thermodynamic, radiation-shielding, and hydrogen-storage properties of CH3NH3MnS3 were investigated using DFT calculations implemented within the Cambridge Serial Total Energy Package (CASTEP) [1]. The exchange-correlation interactions were described using the generalized gradient approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE) functional [2]. Ultrasoft pseudopotential was employed to represent the interactions between valence electrons and ionic cores [3]. The initial crystal structure was fully optimized using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) minimization scheme. The convergence criteria were set to ensure high computational accuracy, with total-energy convergence of 1 × 10-5 eV atom-1, maximum force below 0.03 eV Å-1, maximum stress less than 0.05 GPa, and atomic displacement below 1 × 10⁻3 Å. A plane-wave cutoff energy of 500 eV and an appropriately converged Monkhorst-Pack k-point mesh were used throughout the calculations [4]. Following structural optimization, the electronic properties of CH3NH3MnS3 were examined through calculations of the electronic band structure and density of states (DOS). The band structure was evaluated along the high-symmetry directions of the first Brillouin zone to determine the nature and magnitude of the electronic band gap. Furthermore, total and partial density-of-states analyses were performed to identify the contributions of individual atomic orbitals to the valence-band maximum and conduction-band minimum, thereby providing insight into the electronic interactions governing the material's behavior. The elastic and mechanical properties were determined using the stress-strain approach. Small deformations were applied to the optimized crystal structure, and the resulting stress tensors were used to calculate the independent elastic constants. From these elastic constants, the bulk modulus, shear modulus, and Young's modulus were obtained using the Voigt-Reuss-Hill approximation. Additional mechanical parameters, including Poisson's ratio and the Zener anisotropy factor, were evaluated to investigate the ductility, stiffness, bonding characteristics, and elastic anisotropy of the material. The mechanical stability of the crystal was verified using the appropriate Born stability criteria. The optical response of CH3NH3MnS3 was investigated through calculations of the complex dielectric function. The imaginary part of the dielectric function was obtained from direct electronic transitions between occupied and unoccupied states, while the real part was derived using the Kramers-Kronig transformation. Based on the dielectric function, various optical constants including the refractive index, extinction coefficient, absorption coefficient, optical conductivity, reflectivity, and energy-loss function were calculated over a wide photon-energy range. These calculations provide comprehensive information regarding the interaction of electromagnetic radiation with the material [5, 6]. The absence of imaginary phonon frequencies throughout the Brillouin zone was used as confirmation of dynamical stability. The phonon density of states was subsequently utilized to calculate thermodynamic properties within the quasi-harmonic approximation. Temperature-dependent quantities such as heat capacity, entropy, enthalpy, Gibbs free energy, and Debye temperature were evaluated over a broad temperature range to investigate the thermal behavior of the compound. The radiation-shielding characteristics of CH3NH3MnS3 were assessed using the Phy-X/PSD software package [7, 8]. The mass attenuation coefficient and linear attenuation coefficient were calculated over photon energies ranging from 0.01 to 1000 MeV. Using these parameters, additional shielding quantities such as the half-value layer, tenth-value layer, mean free path, effective atomic number, and effective electron density were determined. Moreover, the exposure buildup factor and energy absorption buildup factor were estimated using the geometric progression fitting method to analyze the influence of multiple scattering events and secondary photon generation on the shielding performance. The hydrogen-storage capability of CH3NH3MnS3 was explored through adsorption-energy and diffusion analyses. Hydrogen adsorption energies were calculated by comparing the total energies of the hydrogen-adsorbed system, pristine structure, and isolated hydrogen molecule. The gravimetric hydrogen-storage capacity was estimated from the maximum hydrogen uptake. Hydrogen migration pathways and diffusion barriers were investigated using NEB method, which identifies the minimum-energy diffusion route between neighboring adsorption sites [9]. The temperature dependence of hydrogen mobility was further examined through Arrhenius-type diffusion calculations. These analyses provide valuable insight into the suitability of CH3NH3MnS3 for hydrogen-storage and energy-related applications. The equation of state for the investigated compounds is given as follows [10]. E V = E 0 + 9 16 B 0 V 0 ( V 0 V ) 2 / 3 - 1 2 1 + 3 4 ( B 0 / - 4 ) ( ( V 0 V ) 2 / 3 - 1 In the Birch-Murnaghan equation of state, E(V) represents the total energy of the compound at a given unit-cell volume V, while E0 is the minimum equilibrium energy. V0 denotes the equilibrium unit-cell volume corresponding to the most stable structure. B0 is the equilibrium bulk modulus, which measures the resistance of the material to compression, whereas B0' represents the pressure derivative of the bulk modulus and describes how the compressibility changes under pressure. The term (V0/V)2/3 describes the relative change in volume with respect to the equilibrium volume. By fitting calculated energy-volume data to this equation, the equilibrium structural and mechanical parameters of the investigated compound can be obtained.