Chemical Physics Letters (v.682, #C)

Contents (iii-x).

Display OmittedA simple nature of charge-transfer (CT) in the prototype complexes D p - F 2 ( D p = NH 3 , H2O) manifests itself in a very close shape of their CT excitation energy curves ω CT ( R ) along the donor-acceptor separation R. It affords a simple orbital description in terms of the CT orbitals (CTOs) obtained with a transformation of the virtual orbitals of the standard local density approximation (LDA). The transferable energy of the relevant CTO as a function of R closely approximates the common shape of ω CT ( R ) , while the height of the individual curve is determined with the ionization potential of D p .

Display OmittedRhodopsins are seven-transmembrane proteins that function as photoreceptors for a variety of biological processes. Their characteristic visible colors make rhodopsins a good model for membrane-embedded proteins. In this study, by utilizing their color changes, we performed comparative studies on the stability of five microbial rhodopsins using the same instruments, procedures and media. As denaturants, we employed four physicochemical stimuli: (i) thermal perturbation, (ii) the water-soluble reagent hydroxylamine, (iii) the detergent sodium dodecyl sulfate, and (iv) the organic solvent ethanol. On the basis of the results, models for stabilization mechanisms in rhodopsins against each stimulus is proposed.

Display OmittedWe present a series of three studies investigating the potential application of high vacuum electrospray deposition to construct molecular electronic devices. Through the use of time of flight secondary ion mass spectrometry we explore the use of this novel deposition technique to fabricating multilayer structures using materials that are compatible with the same solvents and films containing a mixture of molecules from orthogonal solvents. Using X-ray photoelectron spectroscopy we study the deposition of a polymer blend using electrospray and find evidence of preferential deposition of one of the components.
Keywords: Electrospray deposition; ToF-SIMS; XPS; Molecular electronics; Polymers;

Display OmittedWe propose a new class of endofullerene complexes by encapsulating superalkali species (viz. FLi2, OLi3 and NLi4) within C60 and then interacting with superhalogens (viz. BF4, BCl4 and BBr4). Our DFT calculations reveal that all M@C60−BF4 (M = FLi2  < OLi3  < NLi4) endofullerene complexes are stable against complexation and deencapsulation. The first order mean hyperpolarizability (βo) values decrease with the increase in the size of encapsulated superalkalis but increase with the increase in the size of superhalogen. The trend of βo values has been explained by TDDFT calculated parameters for crucial electronic transitions of endofullerene complexes.
Keywords: Endofullerene; Superhalogen; Superalkali; NLO properties; Density functional theory;

Display OmittedEighteen tripeptides that fit into the thermally vibrating active site of cathepsin K were discovered by alternating artificial intelligence and molecular simulation. The 18 tripeptides fit the active site better than the cysteine protease inhibitor E64, and a better inhibitor of cathepsin K could be designed considering these tripeptides. Among the 18 tripeptides, Phe–Arg–Asp and Tyr–Arg–Asp fit the active site the best and their structural similarity should be considered in the design process. Interesting factors emerged from the structure of the decision tree, and its structural information will guide exploration of potential inhibitor molecules for proteases.
Keywords: Protein; Artificial intelligence; Molecular dynamics simulations; Docking simulations;

Display OmittedThe ab initio calculations have shown that the atoms in the beryllium dimer are covalently bound at the low-lying vibrational energy levels with ν  = 0–4, while at the higher levels with ν  = 5–11 the atoms are bonded by the van der Waals forces near the right turning points. The developed ab initio modified EMO potential function, in distinction with the original EMO function, which was used for a description of the experimental vibrational levels, not only has the correct dissociation energy, but also describes all twelve vibrational energy levels with a smaller RMS error of less than 0.4 cm−1.
Keywords: Covalent bonding; Van der Waals bonding; Vibrational energy levels; Beryllium dimer;

Two-color resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of 4-chlorostyrene by Pei Ying Wu; Hsin Hsuan Huang; King Chuen Lin; Wen Bih Tzeng (34-37).
Display OmittedThe first electronic excitation and adiabatic ionization energies of 35Cl and 37Cl 4-chlorostyrene were similar, with values of 33,977 ± 2 and 67,972 ± 5 cm−1, respectively. The general features in the obtained vibronic and cation spectra of the two isotopologues were similar. A frequency shift of 1–5 cm−1 was observed on many active vibrations of the 35Cl and 37Cl isotopologues of 4-chlorostyrene in the S1 and D0 states. This frequency difference at each mode may reflect the degree of Cl atom involvement in the overall vibration.
Keywords: Resonant two-photon ionization; Mass-analyzed threshold ionization; 4-Chlorostyrene; Isotopologues; Vibronic spectrum; Cation spectrum;

Comparative study of semilocal density functionals on solids and surfaces by Yuxiang Mo; Guocai Tian; Jianmin Tao (38-42).
Display OmittedRecently, Tao and Mo (TM) proposed an accurate nonempirical meta-generalized gradient approximation (meta-GGA). To better understand the performance of this functional, here we make a comparative study of the combinations of the TM exchange part with the original TPSS correlation (TMTPSS) and the modified TPSS correlation (TM) on a variety of solids and surfaces. Specifically, we compare the performance of these two functionals on 22 lattice constants and bulk moduli, 30 band gaps of semiconductors, 7 cohesive energies, and surface exchange-correlation energies of simple metals with rs ranging from 2 to 3 bohr.

Structural and thermodynamic investigation of pentoxifylline-cyclodextrin inclusion complex by Charles A.S. Morais; Bruna Lemes Silva; Ângelo M.L. Denadai; Juliana Fedoce Lopes; Frederico B. De Sousa (43-48).
Display OmittedPentoxifylline (PTX) inclusion complex with β-cyclodextrin (β-CD) was investigated by theoretical and experimental methods. Based on the PTX electronic absorption band variation in presence of β-CD and using nuclear magnetic resonance experiments inclusion was verified. Data were confirmed by theoretical UV–Vis by means of TD-DFT calculations, demonstrating that β-CD cavity was able to reduce the oscillator strength of some electronic transitions, and indicating a close range between internal β-CD hydrogens to aliphatic PTX chain. Isothermal titration calorimetry experiments were useful to indicate that inclusion was spontaneous in solution. Additionally, at 298.15 K this inclusion process is enthalpic and entropic driven.
Keywords: Cyclodextrin; Pentoxifylline; Supramolecular structure; Thermodynamic parameters;

Display OmittedThe aim of this study is to investigate the potential of Ti-doped graphene nanoflake (Ti-GNF) for the reduction of CO2 to formic acid by H2. To get a deeper insight into the mechanism of this reaction, the reliable DFT calculations are performed. It is found that the large positive charge on the Ti atom can greatly regulate the surface reactivity of GNF. The formation of the formate group is the rate determining step for the reduction of CO2. The calculated activation energies demonstrate that Ti-GNF could be utilized as an efficient catalyst for the reduction of CO2 to formic acid.
Keywords: Greenhouse gas; CO2 reduction; Formic acid; Graphene; DFT;

Display OmittedA molecular mechanics simulation study of ammonium and amide ion solvation in ammonia is combined with quantum calculations to estimate the pK of the auto-protolysis reaction 2NH3  → NH4 +  + NH2 . While the dielectric constant of liquid ammonia decays with increasing temperature, we find the auto-protolysis reaction to be shifted towards the product side. This is rationalized from discriminating the overall reduction of the polarity of liquid ammonia from local (nearest neighbor molecules) solvent binding to the ammonium and amide ions. Indeed, constant-volume simulations show that NH4 +/NH2 ion coordination prevails heating up to 500 K thus leading to practically constant solvation energy.
Keywords: Ammonia solution; Auto-protolysis; pK constants; Ammonothermal syntheses;

Mass spectrometric study of N2-adsorption on copper cluster cations formed by modulated pulsed power magnetron sputtering in aggregation cell by Keijiro Ohshimo; Isamu Mizuuchi; Kengo Akimoto; Keizo Tsukamoto; Masahide Tona; Hiroaki Yamamoto; Motoyoshi Nakano; Fuminori Misaizu (60-63).
Display OmittedWe have observed gas-phase reactions between N2 molecules and copper cluster cations, Cu n + (n  = 2–17), formed by a modulated pulsed power magnetron sputtering cluster ion source. By introducing N2 gas effusively between the source and an acceleration region of a time-of-flight mass spectrometer in the vacuum chamber, N2-adsorbed copper cluster cations, Cu n N2 +, were observed in mass spectra. The N2-adsorption reactivity of Cu n + was found to be relatively lower at n  ≥ 10 than at the smaller n. The cluster-size dependence of N2-adsorption on Cu n + has a correlation with binding energies between Cu n + and N2 calculated by density functional theory.

Three-dimensional nanoporous MoS2 framework decorated with Au nanoparticles for surface-enhanced Raman scattering by Yingqiang Sheng; Shouzhen Jiang; Cheng Yang; Mei Liu; Aihua Liu; Chao Zhang; Zhen Li; Yanyan Huo; Minghong Wang; Baoyuan Man (64-70).
The three-dimensional MoS2 decorated with Au nanoparticles hybrids for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. The size of nanoparticles can be controlled by varying the concentration of HAuCl4·3H2O. Used R6G as the probe molecule, the prepared 3D MoS2-Au NPs hybrids has shown significant SERS ability. We modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.Display OmittedThe three-dimensional (3D) MoS2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS2-Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS2-Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS2-Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.
Keywords: 3D MoS2-Au NPs hybrids; SERS activity;

Quantum dot sensitized solar cells: Light harvesting versus charge recombination, a film thickness consideration by Xiu Wei Wang; Ye Feng Wang; Jing Hui Zeng; Feng Shi; Yu Chen; Jiaxing Jiang (71-76).
The procedure of the photo-anodes sensitization (a), J-V curve of the cell with the optimized photo-anode thickness (b), M-S plots (c) and charge survival lifetime curves (d) of the cells with the different thickness photo-anodes.Display OmittedSensitizer loading level is one of the key factors determined the performance of sensitized solar cells. In this work, we systemically studied the influence of photo-anode thicknesses on the performance of the quantum-dot sensitized solar cells. It is found that the photo-to-current conversion efficiency enhances with increased film thickness and peaks at around 20 μm. The optimal value is about twice as large as the dye counterparts. Here, we also uncover the underlying mechanism about the influence of film thickness over the photovoltaic performance of QDSSCs from the light harvesting and charge recombination viewpoint.
Keywords: Functional; Electrical properties; Electron microscopy; Semiconductors; Solar energy materials;

Peculiarities of migration and capture of a quantum particle in a chain with traps by Leonid N. Christophorov; Anatoly G. Zagorodny (77-81).
Display OmittedThe presence of sinks-traps at the nodes of a 1D chain disturbs coherency of propagation of a quantum particle in the chain. This results in nontrivial dependences of the quantum yield of capture on the trap intensity and initial placement of the particle. We obtain these dependences in the cases of infinite, semi-infinite, and finite chains with one or two traps.
Keywords: 1D chain; Quantum particle transport; Migration and capture; Quantum yield; Polya's theorem;

An approach to the averaged intermolecular potential field of methane from viscosity by Ailian Zhang; Xiaohong Yang; Shunxi Zhang (82-86).
Display OmittedA novel approach to averaged intermolecular potential field (AIPF) of methane from viscosity was developed. Using symmetric molecular interaction approximation and Maxwell-Boltzmann distribution function of velocity, equations relating the AIPF and viscosity have been derived. Applying the equations to methane, good agreements were found between high quality viscosity data and the equations via fitting method. Then a formula for methane’s AIPF as a function of temperature and density was determined. Obtained results not only give a new method to estimate the AIPF for fluidic system, but also may form a novel base to study the viscosity of other alkane mixtures.
Keywords: Intermolecular potential; Potential field; Viscosity; Methane; Fluidic system;

Explicitly-correlated non-born-oppenheimer calculations of the HD molecule in a strong magnetic field by Ludwik Adamowicz; Monika Stanke; Erik Tellgren; Trygve Helgaker (87-90).
Display OmittedExplicitly correlated all-particle Gaussian functions with shifted centers (ECGs) are implemented within the earlier proposed effective variational non-Born-Oppenheimer method for calculating bound states of molecular systems in magnetic field (Adamowicz et al., 2015). The Hamiltonian used in the calculations is obtained by subtracting the operator representing the kinetic energy of the center-of-mass motion from the total laboratory-frame Hamiltonian. Test ECG calculations are performed for the HD molecule.

Site symmetry approach in the supercell model of carbon-doped ZnO bulk by Robert A. Evarestov; Sergei Piskunov; Yuri F. Zhukovskii (91-95).
Display OmittedCarbon-doped zinc oxide is one of promising materials for technological applications due to its ferromagnetism observed at room temperature. When using the hybrid DFT-HF Hamiltonian based on the PBE0 exchange-correlation functional for large-scale calculations on defective ZnO:C single crystal, we have shown that application of supercell model for carbon impurity located at O site of wurtzite-structured ZnO bulk results in the dependence of calculated formation energy of the point defect (Eform ) on the selected site symmetry of the substituted atom in the supercell. For a more symmetric C 3v site usually used for simulation of defective ZnO structures, values of formation energy per single dopant in supercell essentially exceed those evaluated for less symmetric C 1 and C s sites. On the other hand, each of these three types of Eform does not noticeably differ depending on supercell size if it is large enough to neglect lateral interaction between adjacent dopants. Influence of site symmetry on the electronic structure of C-doped ZnO is discussed too. The suggested approach can be further applied to a wide class of defects in crystalline solids allowing the detailed analysis of electron density localization in a defective crystal and more accurate reproducing the formation energy of point defect.

Synthesis of polyynes by intense femtosecond laser irradiation of SWCNTs suspended in methanol by Junwei Zhao; Yifan Zhang; Yanghao Fang; Zhengfu Fan; Guohong Ma; Yi Liu; Xinluo Zhao (96-100).
Display OmittedPolyyne samples C2nH2 (n = 4–6) were synthesized by irradiating single-wall carbon nanotubes in methanol with intense femtosecond laser pulses. For obtaining isolated polyynes (C8H2, C10H2, and C12H2), the original solution was separated by high performance liquid chromatography. The surface-enhanced Raman scattering spectra of isolated polyynes in Ag colloid have been investigated with naturally drying time, and clear peaks in the region of β band for the isolated C8H2 were observed at 1910 and 1958 cm−1 in the damp-dried Ag colloid samples for the first time.
Keywords: Polyyne; Femtosecond laser irradiation; SWCNTs; Surface-enhanced Raman scattering;

Display OmittedHierarchical β -NaGdF4 nanobundles are synthesized through a facile hydrothermal method with the use of sodium acetate (NaAc). A NaGdF4-GdF3-NaGdF4 products transformation with the increase of fluoride source (NaF) is observed. Results show that NaAc is the key factor in the synthesis of β -NaGdF4 at a low NaF/Gd3+ ratio and NaAc also plays a significant role in the formation of the hierarchical morphology. Meanwhile, the size of nanobundles increases with the increased ratio of NaF/NaAc. With altering the ratio of reactants, dumbbell-like, urchin-like or rod-like β -NaGdF4 nanobundles are obtained. The photoluminescent properties of β -NaGdF4: 2%Eu3+ are also measured.
Keywords: NaGdF4; Nanobundles; Hierarchical; Dumbbell-like; Sodium acetate;

Metastability of the low-lying electronic states of CBr2+: A CASSCF/MRCI study by Igor Araujo Lins; Antonio Ricardo Belinassi; Fernando Rei Ornellas; Tiago Vinicius Alves (108-114).
Display OmittedThe metastability of the low-lying electronic states of CBr2+ correlating with the two lowest dissociation channels was investigated for the first time at a high level theoretical approach, SA-CASSCF/MRCI. Spin-orbit interaction changes substantially the profile of the potential energy curves, specially for the ground (X 2 Σ + ) and first excited (1 2 Π ) states. The second adiabatic ionization energies are also determined and show an excelent agreement with the experimental derived values. Tunneling widths computed for the Ω bound states show that the lowest vibrational levels of components 1/2 are stable against tunneling.

Insight into CH4 formation and chain growth mechanism of Fischer−Tropsch synthesis on θ-Fe3C(0 3 1) by Yifan Wang; Ying Li; Shouying Huang; Jian Wang; Hongyu Wang; Jing Lv; Xinbin Ma (115-121).
Display Omittedθ-Fe3C has been reported to play a key role in C2−C4 olefins production for Fischer−Tropsch synthesis. In this work, (0 3 1) is confirmed as the most exposed facet of θ-Fe3C due to its thermodynamic stability. Investigation on CH4 formation and C1−C1 coupling reveals that CH4 formation exhibits a high effective barrier and CH + CH and CH2  + CH2 are the dominant chain growth pathways. ΔE eff was employed to quantify the selectivity of CH4 and C2+. The high value of ΔE eff indicates the preference of C2+ formation to CH4. These results will help for the design of selective Fe-based FT catalysts.
Keywords: Fischer−Tropsch synthesis; θ-Fe3C; DFT; Selectivity; CH4 formation; C1−C1 coupling;

Effects of head type on the stability of gemini surfactant foam by molecular dynamics simulation by Gang Wu; Congtai Yuan; Xianjing Ji; Hongbing Wang; Shuangqing Sun; Songqing Hu (122-127).
Display OmittedMolecular dynamics simulations have been carried out to study the stability of gemini surfactant foam with different head groups. The results showed that the interaction strength between the polar head groups of the surfactants and water molecules increased from 12-3S-12 (sulfate) system, 12-3Sn-12 (sulfonate) system to 12-3L-12 (carboxylate) system, and the coordination number of water molecules around head increased. From the perspective of energy, the interface formation energy of 12-3L-12 system was smallest, which means that the foam stability was the best. These results indicated that the different head type had a significant effect on the stability of gemini surfactant foam.
Keywords: Head type; Foam stability; Gemini surfactant; Molecular dynamics; Interface formation energy;

Synthesis and photoeletrochemical performance of AuAg@CdS double-walled nanotubes by Shundong Guan; Xiuli Fu; Ying Tang; Zhijian Peng (128-132).
Display OmittedUniform CdS coated AuAg alloyed double-walled nanotubes were successfully fabricated by solvothermal process using Ag nanowires as the template. UV–vis-NIR extinction spectra revealed that the obtained double-walled nanotubes can present an enhanced light absorption ability compared with both pure AuAg alloyed nanotubes and CdS nanowires. Photocurrent and electrochemical impedance spectroscopy measurements indicated that such double-walled structure could significantly extend the lifetime of photo-generated carriers and increase the light-harvesting efficiency of CdS, due to the low charge transfer resistance and a high carrier transfer rate of the double-walled structure. The growth mechanism of such kind of nanotubes was also proposed.
Keywords: AuAg@CdS double-walled nanotubes; Solvothermal synthesis; Growth mechanism; Photoeletrochemical properties;

D-A dyad and D-A-D triad incorporating triphenylamine, benzanthrone and perylene diimide: Synthesis, electrochemical, linear and nonlinear optical properties by Liu Cao; Liang Xu; Dingfeng Zhang; Yecheng Zhou; Yusen Zheng; Qinrui Fu; Xiao-Fang Jiang; Fushen Lu (133-139).
The symmetric D-A-D triads and asymmetric D-A dyads incorporating triphenylamine donor and benzanthrone or perylene diimide acceptor have been designed and synthesized. The photophysical and electrochemical properties, Gaussian calculation and third-order nonlinear optical properties have been studied. Among them, the symmetric D-A-D type molecule with a linear configuration shows the largest 2PA coefficient and 2PA cross section value.Display OmittedTo study the relationship between donor (D)-acceptor (A) structures and the third-order nonlinear optical property, two types of D-A and D-A-D structures based on triphenylamine-substituted chromophores with benzanthrone or perylene diimide (PDI) acceptors have been designed and synthesized. Among them, D-A-D type chromophores with a linear configuration show relatively larger two-photon absorption (2 PA) coefficient and 2 PA cross section value.
Keywords: Non-linear optics; Two-photon absorption; Triphenylamine; Perylene diimide; Benzanthrone;

Preparation and characterization of Ag-doped In2O3 nanoparticles gas sensor by Kanica Anand; Jasmeet Kaur; Ravi Chand Singh; Rengasamy Thangaraj (140-146).
Display OmittedPure and Ag-doped In2O3 nanoparticles are synthesized by the co-precipitation method and are characterized by X-ray diffraction, transmission electron microscopy and photoluminescence spectroscopy. Gas sensing properties of the sensors has been investigated towards methanol, ethanol, acetone and LPG at different operating temperatures. It is found that the sensor response magnitude of the 3% Ag-doped In2O3 nanoparticles sensors is higher to 50 ppm of ethanol at 300 °C, to acetone at 350 °C and to LPG at 400 °C. This is mainly attributed to the large number of oxygen vacancies and defects in doped sensors as corroborated by the photoluminescence studies.
Keywords: In2O3; Nanoparticles; Gas sensor; Ag-doping;

Micelles entrapped Cresyl Violet can selectively detect copper and mercury ions in solution: A fluorescence Correlation Spectroscopy investigation by Nirmal Kumar Das; Subhadip Ghosh; Sunidhi Jaiswal; Anu Tewary; Saptarshi Mukherjee (147-153).
Using single molecule of Fluorescence Correlation Spectroscopy technique we have demonstrated that micelle entrapped Cresyl Violet can be used to selectively and quantitatively detect biologically relevant Cu2+ and Hg2+ ions in solution with a limit of detection of 70 nM and 35 nM, respectively.Display OmittedThe dynamic interaction of Cresyl Violet (CV) in different micellar systems has been demonstrated in single molecular level by FCS studies. The SDS micelle entrapped CV efficiently detected Cu2+ ions in solution with a limit of detection (LOD) of 70 nM, which is further substantiated with the gradual enhancement of the translational motion. The CV entrapped in the DTAB micelles could selectively detect Hg2+ ions in solution with a LOD of 35 nM. The micelle encapsulated CV was effective in detecting these metal ions in real water samples from different sources.
Keywords: Cresyl Violet; Copper ions; Fluorescence Correlation Spectroscopy; Lifetime; Mercury; Metal ion sensing; Surfactants;

Display OmittedAbsolute rate coefficient for the gas phase reaction of OH radical with thiophene has been measured using the laser photolysis (LP) – laser induced fluorescence (LIF) technique. The kinetics measurements were done over the temperature range of 272–353 K and pressure range of 20–30 Torr. The bimolecular rate coefficients obtained were pressure independent in the above pressure range and showed Arrhenius type behaviour which were fitted to the expression k(T) = (4.53 ± 0.55) × 10−12  exp[(250 ± 30)/T] cm3  molecule−1  s−1. The reaction shows weak negative temperature dependence. These results were discussed with available literature and the tropospheric lifetime of thiophene was calculated.

Display OmittedThe finite field method was used to calculate the static first and second hyperpolarizabilities (β and γ) for organic molecules. The dependence of β and γ on the applied electric field strength was investigated and used to determine the optimal field strength for each individual molecule. For γ, we designed a protocol that uses the maximum atomic distance within the molecule along the direction of the applied field to estimate optimal field strengths. However, β is nearly independent of the descriptors we considered, and largely depends on the composition (e.g., the presence of certain functional groups) of the molecule.
Keywords: Hyperpolarizability; Finite field methods; Richardson extrapolation; Error reduction; Quantitative structure property relationships;

C2H4 adsorbed in MOF-74-Mg. (a) Low loading (1:6), (b) Medium loading (1:2), and (c) High loading (1:1). The aqua, gray, red, and white spheres represent magnesium, carbon, oxygen, and hydrogen, respectively.Display OmittedPeriodic boundary condition models are used to investigate the interaction of small hydrocarbons (C2-C4) with MOF-74-Mg/Zn. In contrast to other studies where molecular cluster approaches are used, the complete chemical environment of the framework is included. This allows correcting the binding energies for basis-set superposition error, molecular lateral interaction, zero-point energy, and thermal contributions. As such, the presented results are directly comparable to experimental calorimetric values. This work discusses, for the first time, the origin of the fictitious agreement between binding energies obtained with molecular clusters and experimental heats of adsorption, identifying its origin as due to compensation of errors.
Keywords: MOF; PBC; Light hydrocarbons; Separation; Heats of adsorption; Lateral interaction; Long range forces; DFT;