Density functional theory for responsive hard-sphere fluidsLópez-Molina, J.; Tirado-Miranda, M.; Dzubiella, J.; Moncho-Jordá, A.
2024 Molecular Physics
doi: 10.1080/00268976.2024.2410481
We investigate the equilibrium properties of responsive hard-sphere fluids, where the particle size is a coarse-grained property that fluctuates within an internal free-energy landscape, responding to changes in concentration or the application of external fields. For this purpose, we employ a generalised density functional theory for responsive colloids based on the fundamental measure theory for polydisperse hard-sphere mixtures. We find that increasing particle softness yields a substantial reduction in mean particle size, volume fraction and pressure. We also examine the density profiles and size segregation of responsive hard-sphere fluids subjected to three representative external potentials: a planar hard wall, gravitational and Archimedes buoyant fields. We observe that increasing stiffness or particle concentration enhances density oscillations, converging to the behaviour of a monodisperse fluid. In a gravitational field, size segregation occurs, with smaller particles accumulating at the bottom due to sedimentation. This effect is more pronounced when the Archimedes force is included, causing larger colloids to accumulate at the top, leading to density oscillations in this region that intensify with particle softness, an effect not observed in monodisperse systems. Finally, we demonstrate that responsiveness leads to distinct behaviour compared to conventional polydisperse non-responsive fluids, in which particle compression is not allowed.
A DFT study on antimonene as a drug delivery vehicle for carmustine, lomustine and nitrosourea anticancer drugsKhalid, Swera; Majeed, Areeba; Bano, N.; Ali, Syed Mansoor; Ashraf, Naveed; Gul, Muhammad; Isa Khan, Muhammad
2024 Molecular Physics
doi: 10.1080/00268976.2024.2413008
We used antimonene (Sb) as a delivery vehicle for transporting drugs like Carmustine (CMT), Lomustine (LOMU) and Nitrosourea (NU) in both gaseous and liquid states. The Sb nanosheet structure is stable, and its potential for drug adsorption has been investigated in both parallel and perpendicular directions. The parallel configuration is most stable with a higher adsorption energy of −1.18 eV, −0.63 eV and −1.14 eV for LOMU, CMT and NU respectively. We investigated structural parameters, electronic properties, work function and chemical reactivity. Only NU alters the Sb’s semiconductor behaviour to metallic and has the shortest recovery time in the parallel direction. Hirshfield charge analysis revealed that nanosheet displays electron accepting properties, whereas drugs act as electron donors. The decreased work function for CMT and LOMU enhances substrate activity, indicating stronger interactions that may improve drug delivery. We confirmed the drug’s effective interaction with amino acids without impairing proteins. Furthermore, calculated results predicted a minimal acidic environment of malignant growth, CM, NU and LOMU drugs could start to release from the Sb surface without significantly altering the structural properties. This study illustrates how Sb nanosheet holds promise as an effective carrier for drug delivery in biomedical applications.
Quantitative structure-property relationship of glass transition temperatures for organic compoundsYu, Xinliang
2024 Molecular Physics
doi: 10.1080/00268976.2024.2413005
The glass transition temperatures (T gs) of materials used in the manufacture of organic light-emitting diodes (OLEDs) determine their thermal stability. Three Dragon descriptors, TPC, RBF and TDB04s, were adopted to develop quantitative structure-property relationships (QSPR) for the prediction of the T gs of 66 compounds (Data Set I) for OLED application, by applying random forest (RF) and support vector machine (SVM). The RF Model A, based on a training set (44 compounds), was validated with a test set (22 compounds). The RF Model A possesses a coefficient of determination R 2 of 0.942 and a root mean square (rms) error of 10.750 K for the training set and R 2 of 0.909 and rms error of 11.102 K for the test set, which are more accurate than the results from the SVM model. The RF Model A was further validated with 63 OLED molecules (Data Set II). Moreover, the three Dragon descriptors (TPC, RBF and TDB04s) were used to build another T g QSPR model (named RF Model B) for a large dataset of 1934 OLED molecules (Data Set III), which achieved rms errors of 16.79 K for Data Set III, 22.89 K for Data Set I and 20.17 K for Data Set II.
Optimised structural, electronic, optical and mechanical properties of SrTiO3-xHx for photovoltaic applications: a DFT insightZaman, M.; Rehman, M. A.; Zeba, I.; Zafar, Sana; Gillani, S. S. A.
2024 Molecular Physics
doi: 10.1080/00268976.2024.2410483
Density Functional Theory (DFT) computations, by CASTEP code with GGA-PBE correlation functional, for SrTiO3-xHx have been carried out to compute elastic, mechanical, structural, electronic, and optical characteristics of SrTiO3-xHx perovskite hydride material at varied levels of replacements (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0). With the doping of hydrogen, the structure changed from cubic to orthorhombic and then tetragonal. Elastic parameters and negative value of formation energies demonstrate the durability and formability of these materials. It is established that these compounds are brittle by examining the B/G ratio and Poisson ratio. A bandgap is increased from 1.791 eV to 2.441 eV as dopant concentration rises, changing the semiconductor's nature from indirect to direct. Additionally, a detailed explanation of the optical properties for photons in the energy spectrum of 0–10 eV was provided dielectric functions, refractive indices, extinction coefficients, and 0–50 eV were provided including reflectance, absorbance, and energy loss. By increasing hydrogen doping, the highest absorption peak in the visible region is observed for x = 2.1, which shows that SrTiO3-xHx perovskite hydride has revealed stronger potential for photovoltaic applications.
Quantum-chemical study of atomic X30 trefoil knots with X = {H, He, Li, Be, B, C}*Ferrer, Maxime; Burgos, José I.; Klein, Douglas J.; Oliva-Enrich, Josep M.
2024 Molecular Physics
doi: 10.1080/00268976.2024.2409929
Quantum-chemical computations were carried out for a series of circumferences (unknots), trefoil and toric trefoil knots of X30 systems, with X with atomic numbers Z = {1-6}. Relaxed structures lead to different configurations, with the striking cases of C30 and B30, with the former leading to a relaxed trefoil knot and the latter relaxing to a Möbius band, both corresponding to energy minima.
A DFT study of µ4-Hg bridge compoundsVilarrubias, Pere
2024 Molecular Physics
doi: 10.1080/00268976.2024.2409930
Organometallic compounds with µ4-Hg bridge were studied using DFT. The electronic structure of some representative compounds such as Hg[Os3(µCl)(CO)10]2 and Hg[Ru3(µC≡C-CH3)(CO)9]2 and their derivatives were described. Some characteristic electronic transitions were assigned using TDDFT. Finally, certain chemical reactions of these compounds were studied. An estimation of the energies of the reaction is provided using various functionals. Processes such as the gain of electrons or the substitution of Hg by Zn or Cd were found to be energetically favourable.
Application of the flexible and polarisable hydration ion model to study Th(IV) aqueous solutionsPappalardo, Rafael R.; Sánchez Marcos, E.; Martínez, José M.
2024 Molecular Physics
doi: 10.1080/00268976.2024.2412711
Th(IV) hydration in aqueous solution is studied by means of molecular dynamics simulations based on a polarisable Th(IV)- $ {\rm H}_2{\rm O} $ H 2 O interaction potential developed in the framework of the hydrated ion concept. Molecular Dynamics (MD) simulations provide as the only in-solution representative motif the ennea-aqua ion, $ [{\rm Th}({\rm H}_2{\rm O})_9]^{4+} $ [ Th ( H 2 O ) 9 ] 4 + , with first shell water molecules at an average distance of 2.47 Å from the ion, in accordance with most of the experimental estimates. A well-defined second hydration shell is also identified, hosting ca. 19 solvent molecules at 4.65 Å. Non-structural aspects of the Th(IV) hydration phenomenon, such hydration enthalpy and ion diffusion are well reproduced by the simulation results. The analysis of the O-Th-O angle distribution suggests that the capped square antiprism arrangement prevails over the trigonal tricapped prism. The well-balanced definition of the ion–water and water–water interactions in such a demanding ion neighbourhood is confirmed by the EXAFS and XANES spectroscopies. The theoretical spectra, computed from the MD trajectory, are in fine agreement with some of the experimentally recorded. The sensitivity of the XAS spectroscopy to structural changes confirms how the presented potential manages in a proper way the response of the water molecules to the highly polarising electric field generated by the tetravalent ion.
First-principles calculations to investigate thermodynamic, mechanical and electronic properties of Penta-C72 carbon under pressure effectArjun, P.; Nagarajan, V.; Chandiramouli, R.
2024 Molecular Physics
doi: 10.1080/00268976.2024.2411329
The current work explores the mechanical characteristics, band structure modifications, elastic constant changes, and anisotropy of the carbon allotrope Penta-C72 at high pressure. First-principles simulations were used to analyse the structural features, stability, electronic, mechanical, and thermodynamic properties of Penta-C72, a metastable sp3 -bonded structure made up of carbon pentagons joined by bridge-like connections. The structural and dynamical stability of Penta-C72 under high pressure is confirmed using formation energy, phonon band maps, and thermodynamic properties. Besides, Born's mechanical stability criterion is fulfilled based on the elastic constants of Penta-C72, indicating its mechanical stability. Also, the anisotropic mechanical behaviour is shown by the material. Using the Reuss, Voigt, and Hill approximations, the elastic moduli under high pressure were computed, including bulk modulus (K), shear modulus (G), and Young's modulus (E). Besides, Penta-C72 exhibits a rise in anisotropy and moduli with increasing pressure. This investigation explores the changes in the band gap upon variation in the pressure. It is observed that there is a transition from semiconducting to metallic property above 10 GPa. Beyond 10 GPa, the material exhibits metallic behaviour. The study emphasizes that Penta-C72’s exceptional mechanical stability, directional anisotropy, and customisable electronic characteristics make it a strong contender for various engineering applications.
Nucleation of multi-species crystals: methane cleatrate hydrates, a playground for classical force modelsLauricella, Marco; Ciccotti, Giovanni; Meloni, Simone
2024 Molecular Physics
doi: 10.1080/00268976.2024.2410484
Nucleation and growth of methane clathrate hydrates is an exceptional playground to study crystallisation of multi-component, host-guest crystallites when one of the species forming the crystal, the guest, has a higher concentration in the solid than in the liquid phase. This adds problems related to the transport of the low concentration species, here methane. A key aspect in the modelling of clathrates is the water model employed in the simulation. In previous articles, we compared an all-atom force model, TIP4P/Ewald, with a coarse grain one, which is highly appreciated for its computational efficiency. Here, we perform a complementary analysis considering three all-atoms water models: TIP4P/Ewald, TIP4P/ice and TIP5P. A key difference between these models is that the former predicts a much lower freezing temperature. Intuitively, one expects that to lower freezing temperatures of water correspond to lower water/methane–methane gas–clathrate coexistence ones, which determines the degree of supercooling and the degree of supersaturation. Hence, in the simulation conditions, 250 K (500 atm, and fixed methane molar fraction), one expects computational samples made of TIP4P-ice and TIP5P, with a similar freezing temperature ( $ T_f \sim 273 $ T f ∼ 273 K), to be more supersaturated with respect to the case of TIP4P-Ew ( $ T_f \sim 245 $ T f ∼ 245 K), and crystallisation to be faster. Surprisingly, we find that while the nucleation rate is consistent with this prediction, growth rate with TIP4P-ice and TIP5P is much slower than with TIP4P-Ew. The latter was attributed to the slower reorientation of water molecules in strong supercooled conditions, resulting in a lower growth rate. This suggests that the freezing temperature is not a suitable parameter to evaluate the adequacy of a water model.