Dimeric vs bidimeric cells for molecular quantum cellular automata composed of oxidized norbornadiene and its polycyclic derivatives.

Quantum Dot Cellular Automata (QCA) is an emerging trend in the field of nanoelectronics, and computing can be regarded as an alternative to the traditional complementary metal-oxide-semiconductor technology. The paper is devoted to the study of the key functional properties of the cells for molecular QCA based on mixed valence molecules. The theoretical results for the heat dissipation under the conditions of the fast nonadiabatic switching event and cell-cell response function are obtained in the framework of the quantum-mechanical vibronic approach. These results are parameterized using the previous reliable ab initio calculations performed for oxidized norbornadiene and its polycyclic derivatives with variable lengths of the bridge. The comparative analysis of the dimeric and bidimeric molecular cells composed of these compounds is given. It is underlined that the conditions of a strong non-linear response and a low heat release are contradictory. However, despite this problem, a parametric regime is proposed, which provides a low heat release in combination with a strong nonlinear response of the working cell to the electric field induced by the polarized driver cell.

Theoretical insight into clocking in a molecular mixed-valence cell of quantum cellular automata through the vibronic approach.

In this article, we develop a vibronic theory of clocking in molecular quantum cellular automata (QCA). The clocking mechanism is considered for a trigonal trimeric mixed-valence (MV) system with one mobile electron, which is shown to act as the dimeric unit encoding binary information (Boolean states 0 or 1) coupled to a third redox center (Null state). The model includes the electron transfer between the three centers; vibronic coupling of the mobile charge with the "breathing" modes, forming a double degenerate Jahn-Teller vibration of the molecular triangle; and two electric fields, one collinear to the dimeric unit, which controls the binary states, and the other perpendicular to this unit, performing clocking. In the framework of the adiabatic approximation, the potential surface of the trimeric system has been studied and the condition determining switching and clocking has been analyzed in terms of the two controlling fields and the vibronic and transfer parameters. A thorough understanding of the site populations is achieved through the quantum-mechanical solution of the vibronic problem, maintaining the adiabatic condition for the controlling fields. It is shown that a MV trimer can act as a molecular clocked QCA cell, with favorable conditions being a positive electron transfer parameter and sufficiently strong vibronic coupling.

Nitrogen Reduction to Ammonia on a Fe16 Nanocluster: A Computational Study of Catalysis.

The sequence of elementary steps leading to reductive ammonia formation from N2 and H2 catalyzed by a Fe16 cluster is studied using generalized gradient approximation density functional theory and an all-electron basis set of triple-ζ quality. The computational methods are validated by comparison to experimental data such as binding energies where possible. First, the associative and dissociative attachment of N2 to Fe16 is considered, followed by exploration of the pathways leading to distal (Fe16-N-NH2) and enzymatic (NFe16-NH2) formation of an amino group. Next, the pathways leading to NH3 formation in both distal and enzymatic cases are examined. Two mechanisms for NH3 detachment have been discovered. An interesting peculiarity of the pathways is that they often proceed with total spin fluctuations, which are related to the rupture and formation of bonds on the surface of the catalyst over the course of the reactions. The reaction Fe16 + N2 + 2H2 → Fe16NH + NH3 is found to be exothermic by 1.02 eV (93.8 kJ/mol).

Spin polarization effects in trigonal mixed-valence complexes exhibiting double exchange supported by external spin-cores.

The theory of the magnetic coupling between the localized spins, mediated by the mobile excess electron, is generalized to the case of a trigonal, six-center, four-electron molecule with partial valence delocalization. The combination of the electron transfer occurring within the valence-delocalized subsystem and the interatomic exchange producing coupling of the spin of the mobile electron of valence-delocalized fragment with the three localized spins forming the valence-localized subsystem leads to the appearance of a special kind of double exchange (DE), termed the "external core double exchange" (ECDE), in order to distinguish such DE from the conventional "internal core double exchange" for which the mobile electron is coupled with the spin-cores on the same center via the intra-atomic exchange. The effect of the ECDE on the ground spin state of the considered trigonal molecule is compared with earlier reported effect produced by DE in the four-electron, mixed-valence (MV) trimer. A high diversity of the ground spin states is revealed, depending on the relative magnitudes and signs of the electron transfer and interatomic exchange parameters, with part of these states not appearing to be the ground states in a trigonal trimer exhibiting DE. We briefly discuss some examples of trigonal MV systems from the point of view of the possibility to have different combinations of signs of the transfer and exchange parameters and, accordingly, different ground spin states. The tentative role of the considered systems in molecular electronics and spintronics is also noticed.

Exploring the Limits: Degradation Behavior of Lead Halide Perovskite Films under Exposure to Ultrahigh Doses of γ Rays of Up to 10 MGy.

Herein, we show that thin films of MAPbI3, FAPbI3, (CsMA)PbI3, and (CsMAFA)PbI3, where MA and FA are methylammonium and formamidinium cations, respectively, tolerate ultrahigh doses of γ rays approaching 10 MGy without significant changes in their absorption spectra. However, among the studied materials, FAPbI3 was the only one that did not form metallic lead due to its extreme radiation hardness. Infrared near-field optical microscopy revealed the radiation-induced depletion of organic cations from the grains of MAPbI3 and their accumulation at the grain boundaries, whereas FAPbI3 on the contrary lost FA cations from the grain boundaries. The multication (CsMAFA)PbI3 perovskite underwent a facile phase segregation to domains enriched with MA and FA cations, which is a principally new radiation-induced degradation pathway. Our findings suggest that the radiation hardness of the rationally designed perovskite semiconductors could go far beyond the impressive threshold of 10 MGy we set herein for FAPbI3 films, which opens many exciting opportunities for practical implementation of these materials.

Suppressed Layered-to-Spinel Phase Transition in δ-MnO2 via van der Waals Interaction for Highly Stable Zn/MnO2 Batteries.

Although birnessite-type manganese dioxide (δ-MnO2 ) with a large interlayer spacing (≈7 Å) is a promising cathode candidate for aqueous Zn/MnO2 batteries, the poor structural stability associated with Zn2+ intercalation/deintercalation limits its further practical application. Herein, δ-MnO2 ultrathin nanosheets are coupled with reduced graphene oxide (rGO) via van der Waals (vdW) self-assembly in a vacuum freeze-drying process. It is interesting to find that the presence of vdW interaction between δ-MnO2 and rGO can effectively suppress the layered-to-spinel phase transition in δ-MnO2 during cycling. As a result, the coupled δ-MnO2 /rGO hybrid cathode with a sandwich-like heterostructure exhibits remarkable cycle performance with 80.1% capacity retained after 3000 cycles at 2.0 A g-1 . The first principle calculations demonstrate that the strong interfacial interaction between δ-MnO2 and rGO results in improved electron transfer and strengthened layered structure for δ-MnO2 . This work establishes a viable strategy to mitigate the adverse layered-to-spinel phase transition in layered manganese oxide in aqueous energy storage systems.

Spin-Crossover and Slow Magnetic Relaxation Behavior in Hexachlororhenate(IV) Salts of Mn(III) Complexes [Mn(5-Hal-sal2323)]2[ReCl6] (Hal = Cl, Br).

The cationic complexes of Mn(III) with the 5-Hal-sal2323 (Hal = Cl, Br) ligands and a paramagnetic doubly charged counterion [ReCl6]2- have been synthesized: [Mn(5-Cl-sal2323)]2[ReCl6] (1) and [Mn(5-Br-sal2323)]2[ReCl6] (2). Their crystal structures and magnetic properties have been studied. These isostructural two-component ionic compounds show a thermally induced spin transition at high temperature associated with the cationic subsystem and a field-induced slow magnetic relaxation of magnetization at cryogenic temperature, associated with the anionic subsystem. The compounds are the first examples of the coexistence of spin crossover and field-induced slow magnetic relaxation in the family of known [MnIII(sal2323)] cationic complexes with various counterions.

Novel Type of Tetranitrosyl Iron Salt: Synthesis, Structure and Antibacterial Activity of Complex [FeL'2(NO)2][FeL'L"(NO)2] with L'-thiobenzamide and L"-thiosulfate.

In this work a new donor of nitric oxide (NO) with antibacterial properties, namely nitrosyl iron complex of [Fe(C6H5C-SNH2)2(NO)2][Fe(C6H5C-SNH2)(S2O3)(NO)2] composition (complex I), has been synthesized and studied. Complex I was produced by the reduction of the aqueous solution of [Fe2(S2O3)2(NO)2]2- dianion by the thiosulfate, with the further treatment of the mixture by the acidified alcohol solution of thiobenzamide. Based on the structural study of I (X-ray analysis, quantum chemical calculations by NBO and QTAIM methods in the frame of DFT), the data were obtained on the presence of the NO…NO interactions, which stabilize the DNIC dimer in the solid phase. The conformation properties, electronic structure and free energies of complex I hydration were studied using B3LYP functional and the set of 6-31 + G(d,p) basis functions. The effect of an aquatic surrounding was taken into account in the frame of a polarized continuous model (PCM). The NO-donating activity of complex I was studied by the amperometry method using an "amiNO-700" sensor electrode of the "inNO Nitric Oxide Measuring System". The antibacterial activity of I was studied on gram-negative (Escherichia coli) and gram-positive (Micrococcus luteus) bacteria. Cytotoxicity was studied using Vero cells. Complex I was found to exhibit antibacterial activity comparable to that of antibiotics, and moderate toxicity to Vero cells.

Magnetically bistable cobalt-dioxolene complexes with a tetradentate N-donor base.

Synthesis and magnetic characterization of a family of cobalt-dioxolene complexes [(Me2TPA)Co(36-DBCat)] (1), [(Me2TPA)Co(36-DBCat)](PF6) (2) and [(Me2TPA)Co(diox-(OMe)3)](BPh4) (3) (Me2TPA = bis(6-methyl-2-pyridyl)methyl-(2-pyridylmethyl)amine; 36-DBCat = dianion of 3,6-di-tert-butylcatechol; diox-(OMe)3 - 2,5-di-tert-butyl-3,3,4-trimethoxy-6-oxocyclohexa-1,4-dienolate) is reported. The neutral complex 1 is found to form hexa- (CoO2N4, 1a) and pentacoordinated (CoO2N3, 1b) isomers. Variable temperature single crystal X-ray diffraction analysis of 1a and 1b clearly indicates the presence of the high-spin divalent metal ion and the dianionic catecholate form of the dioxolene ligand. Oxidation of 1 by ferrocenium hexafluorophosphate results in the formation of the ionic octahedral complex 2, demonstrating thermally induced valence-tautomeric transition (ls-CoIII-36-DBCat ⇄ hs-CoII-36-DBSQ) in the solid state with T1/2 = 175 K (36-DBSQ = radical-anionic semiquinonate form of the redox-ligand). In contrast, aerial oxidation of 1 is accompanied by changes in the structure of dioxolene resulting in oxocyclohexadienolate ligand and the formation of an ionic complex of high-spin divalent cobalt (3). Compounds 1a, 1b, and 3 are found to demonstrate a field-induced single-ion magnet behavior. The analysis of the electronic structures of 1, 2 and 3 with the aid of DFT and SA-CASSCF/NEVPT2 calculations is also given.

Vibronic recovering of functionality of quantum cellular automata based on bi-dimeric square cells with violated condition of strong Coulomb repulsion.

Strong Coulomb repulsion between the two charges in a square planar mixed-valence cell in quantum cellular automata (QCA) allows us to encode the binary information in the two energetically beneficial diagonal distributions of the electronic density. In this article, we pose a question: to what extent is this condition obligatory for the design of the molecular cell? To answer this question, we examine the ability to use a square-planar cell composed of one-electron mixed valence dimers to function in QCA in a general case when the intracell Coulomb interaction U is not supposed to be extremely strong, which means that it is comparable with the characteristic electron transfer energy (violated strong U limit). Using the two-mode vibronic model treated within the semiclassical (adiabatic) and quantum-mechanical approaches, we demonstrate that strong vibronic coupling is able to create a considerable barrier between the two diagonal-type charge configurations, thus ensuring bistability and polarizability of the cells even if the Coulomb barrier is not sufficient. The cases of weak and moderate Coulomb repulsion and strong vibronic coupling are exemplified by consideration of the cation radicals of the two polycyclic derivatives of norbornadiene [C12H12]+ and [C17H16]+ with the terminal C=C chromophores playing the role of redox sites. By using the detailed ab initio data, we reveal the main characteristics of the bi-dimeric cells composed of these molecules and illustrate the pronounced effect of the vibronic recovery clearly manifesting itself in the shape of the cell-cell response function. Revealing such "vibronic recovery" of strong localization when the strong U limit is violated suggests a way to a significant expansion of the class of molecular systems suitable as QCA cells.

Mechanisms of Complete Dissociation of CO2 on Iron Clusters.

Dissociation of CO2 on iron clusters was studied by using semilocal density functional theory and basis sets of triple-zeta quality. Fe2 , Fe4 , and Fe16 clusters were selected as the representative host clusters. When searching for isomers of Fen CO2 , n=2, 4 and 16 corresponding to carbon dioxide attachment to the host clusters, its reduction to O and CO, and to the complete dissociation, it was found that the total spin magnetic moments of the lowest energy states of the isomers are often quenched with respect to those of initial reagents Fen +CO2 . Dissociation pathways of the Fe2 +CO2 , Fe4 +CO2 , and Fe16 +CO2 reactions contain several transition states separated by the local minima states; therefore, a natural question is where do the spin flips occur? Since lifetimes of magnetically excited states were shown to be of the order of 100 fs, the search for the CO2 dissociation pathways was performed under the assumption that magnetic deexcitation may occur at the intermediate local minima. Two dissociation pathways were obtained for each Fen +CO2 reaction using the gradient-based methods. It was found that the Fe2 +CO2 reaction is endothermic with respect to both reduction and complete dissociation of CO2 , whereas the Fe4 +CO2 and Fe16 +CO2 reactions are exothermic to both reduction and complete dissociation of carbon dioxide. The CO2 reduction was found to be more favorable than its complete dissociation in the Fe4 case.

Nanoscale Visualization of Photodegradation Dynamics of MAPbI3 Perovskite Films.

Herein, we report the nanoscale visualization of the photochemical degradation dynamics of MAPbI3 (MA = CH3NH3+) using infrared scattering scanning near-field microscopy (IR s-SNOM) combined with a series of complementary analytical techniques such as UV-vis and FTIR-spectroscopy, XRD, and XPS. Light exposure of the MAPbI3 films resulted in a gradual loss of MA+ cations starting from the grain boundaries at the film surface and slowly progressing toward the center of the grains and deeper into the bulk perovskite phase. The binary lead iodide PbI2 was found to be the major perovskite photochemical degradation product under the experimental conditions used. Interestingly, the formation of the PbI2 skin over the perovskite grains resulted in a largely enhanced photoluminescence, which resembles the effects observed for core-shell quantum dots. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved degradation dynamics of perovskite absorbers and revealing the associated material aging pathways.

Towards the design of molecular cells for quantum cellular automata: critical reconsideration of the parameter regime for achieving functionality.

In this article, we present a critical discussion of the parametric regimes required for reaching the functionality of the two-electron square-planar tetrameric mixed-valence (MV) complexes as molecular cells in quantum cellular automata (QCA). Previous studies on molecular QCA were restricted by the limit case of strong Coulomb interaction that was supposed to be the only way to ensure such two key requirements for functioning QCA cells as bistability and switchability. It was thus assumed that the site-to-site electron transfer energy t should be much smaller than the energy U of the Coulomb repulsion between the two excess electrons (strong-U limit defined by the inequality U ≫ t). Unlike those studies, here, we develop a generalized theoretical approach within which no restricting assumptions are implied on the relative strength of the intracell Coulomb interaction, electron transfer, the vibronic coupling with "breathing" modes of redox sites and the external electrostatic field of the driver cell acting on the working cell. We demonstrate that dominating Coulomb repulsion is not the only source of bistability and switchability, but such key features of QCA cell can be reached even in systems in which the strong-U limit is violated, provided that the vibronic coupling is strong enough. Such a reconsideration of the parameter regime for achieving proper functionality is expected to essentially enlarge the family of MV molecules, which can be used as molecular QCA cells.

Evolution of Ferromagnetic and Antiferromagnetic States in Iron Nitride Clusters FenN and FenN2 (n = 1-10).

First-principles density functional theory calculations on neutral and singly negatively and positively charged iron clusters Fen and iron nitride clusters FenN and FenN2 (n = 1-10) in the range of 1 ≤ n ≤ 10 revealed that there is a strong competition between ferromagnetic and antiferromagnetic states especially in the FenN20,±1 cluster series. This phenomenon was related to superexchange via a bridging N atom between two iron atoms in the FenN20,±1 cluster series and to a double superexchange effect via a Fe atom shared by two N atoms in the FenN20,±1 series. A thorough examination of the structure-energy-spin state relationships in these clusters is conducted, leading to new insights and confirmation of available experimental results on structural parameters and dissociation energetics. The bond energies of both nitrogen atoms in the FenN2 series are approximately the same. They weakly depend on the charge of the host cluster and fluctuate around 5.5 eV when moving along the series. The energy of N2 desorption is relatively small; it varies by about 1.0 eV and depends on the charge of the cluster. The experimental finding that N2 dissociates on the Fen+ clusters beginning with n = 4 was supported by the results of our computations. Our computed values of the Fen+-N bonding energies agree with the experimental data within the experimental uncertainty bars. It was found that the attachment of one or two N atoms does not seriously affect the polarizability, electron affinity, or ionization energy of the host iron clusters independent of the charge.

Insight Into The Spin-Vibronic Problem of a Mixed Valence Magnetic Molecular Cell for Quantum Cellular Automata.

The effects of the vibronic coupling in quantum cellular automata (QCA) based on the square planar mixed valence (MV) molecular cells comprising four paramagnetic centers (spin cores) and two excess mobile electrons are analyzed in the important particular case when the Coulomb energy gap between the ground antipodal diagonal-type two-electron configurations and the excited side-type configurations considerably exceeds both the one-electron transfer parameter (strong U-limit) and the vibronic stabilization energy. Under such conditions the developed model involves the second-order double exchange, the Heisenberg-Dirac-Van Vleck (HDVV) exchange and the vibronic coupling of the excess electrons with the molecular B1g -vibration composed of four full-symmetric local vibrations. The latter interaction is shown to significant amplify the ability of the electric field produced by the driver-cell to polarize the excess electrons in the working cell, which can be termed "the effect of the vibronic enhancement of the cell-cell interaction". This effect leads to a redetermination of the conditions for switching between different spin-states, as well as to a significant change in the shapes of the cell-cell response functions. The obtained results demonstrate the importance of the vibronic coupling in all aspects (such as description of a free cell and cell-cell response) of the theory of molecular QCA based on MV clusters.

Toward multifunctional molecular cells for quantum cellular automata: exploitation of interconnected charge and spin degrees of freedom.

We discuss the possibility of using mixed-valence (MV) dimers comprising paramagnetic metal ions as molecular cells for quantum cellular automata (QCA). Thus, we propose to combine the underlying idea behind the functionality of QCA of using the charge distributions to encode binary information with the additional functional options provided by the spin degrees of freedom. The multifunctional ("smart") cell is supposed to consist of multielectron MV dn-dn+1-type (1 ≤ n ≤ 8) dimers of transition metal ions as building blocks for composing bi-dimeric square planar cells for QCA. The theoretical model of such a cell involves the double exchange (DE), Heisenberg-Dirac-Van Vleck (HDVV) exchange, Coulomb repulsion between the two excess electrons belonging to different dimeric half-cells and also the vibronic coupling. Consideration is focused on the topical case in which the difference in Coulomb energies of the two excess electrons occupying nearest neighboring and distant positions significantly exceeds both the electron transfer integral and the vibronic energy. In this case the ground spin-state of the isolated square cell is shown to be the result of competition of the second-order DE producing a ferromagnetic effect and the HDVV exchange that is assumed to be antiferromagnetic. In order to reveal the functionality of the magnetic cells, the cell-cell response function is studied within the developed model. The interaction of the working cell with the polarized driver-cell is shown to produce an antiferromagnetic effect tending to suppress the ferromagnetic second-order DE. As a result, under some conditions the electric field of the driver cell is shown to force the working cell to exhibit spin-switching from the state with maximum dimeric spin values to that having minimal spin values.

Temperature Dynamics of MAPbI3 and PbI2 Photolysis: Revealing the Interplay between Light and Heat, Two Enemies of Perovskite Photovoltaics.

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

Partial Substitution of Pb2+ in CsPbI3 as an Efficient Strategy To Design Fairly Stable All-Inorganic Perovskite Formulations.

All-inorganic lead halide perovskites, for example, CsPbI3, are becoming more attractive for applications as light absorbers in perovskite solar cells because of higher thermal and photochemical stability as compared to their hybrid analogues. However, a specific drawback of the CsPbI3 absorber consists of the rapid phase transition from black to yellow nonphotoactive phase at low temperatures (e.g., <100 °C), which is accelerated under exposure to light. Herein, an experimental screening of an unprecedently large series (>30) of metal cations in a wide range of concentration has allowed us to establish a set of Pb2+ substitutes, facilitating the crystallization of the photoactive black CsPbI3 phase at low temperatures. Importantly, the appropriate Pb2+ substitution with Ca2+, Sr2+, Ce3+, Nd3+, Gd3+, Tb3+, Dy2+, Er3+, Yb2+, Lu3+, and Pt2+ cations has led to a spectacular enhancement of the film stability under realistic solar cell operation conditions (∼1 sun equivalent light exposure, 50 °C). Optoelectronic, structural, and morphological effects of partial Pb2+ substitution were investigated, providing a deeper insight into the processes underlying the stabilization of the CsPbI3 films. Several CsPb1-xMxI∼3 systems were evaluated as absorber materials in perovskite solar cells, demonstrating encouraging light power conversion efficiency of 11.4% in preliminary experiments. The obtained results feature the potential of designing efficient and stable all-inorganic perovskite solar cells using novel absorber materials rationally designed via compositional engineering.

Dissociation of dinitrogen on iron clusters: a detailed study of the Fe16 + N2 case.

The coalescence of two Fe8N as well as the structure of the Fe16N2 cluster were studied using density functional theory with the generalized gradient approximation and a basis set of triple-zeta quality. It was found that the coalescence may proceed without an energy barrier and that the geometrical structures of the resulting clusters depend strongly on the mutual orientations of the initial moieties. The dissociation of N2 is energetically favorable on Fe16, and the nitrogen atoms share the same Fe atom in the lowest energy state of the Fe16N2 species. The attachment of two nitrogen atoms leads to a decrease in the total spin magnetic moment of the ground-state Fe16 host by 6 µB due to the peculiarities of chemical bonding in the magnetic clusters. In order to gain insight into the dependence of properties on charge and to estimate the bonding energies of both N atoms, we performed optimizations of Fe16N and the singly charged ions of both Fe16N2 and Fe16N. It was found that the electronic properties of the Fe16N2 cluster, such as electron affinity and ionization energy, do not appreciably depend on the attachment of nitrogen atoms but that the average binding energy per atom changes significantly. The lowering in total energy due to the attachment of two N atoms was found to be nearly independent of charge. The IR and Raman spectra were simulated for Fe16N2 and its ions, and it was found that the positions of the most intense peaks in the IR spectra strongly depend on charge and therefore present fingerprints of the charged states. The chemical bonding in the ground-state Fe16N20,±1 species was described in terms of the localized molecular orbitals.

A parametric two-mode vibronic model of a dimeric mixed-valence cell for molecular quantum cellular automata and computational ab initio verification.

In this article we propose a two-mode vibronic model of a molecular cell for quantum cellular automata. The molecular cell is represented by a mixed-valence dimeric cluster in which the mobile electron is coupled to two kinds of molecular vibrations. The first type of vibration is represented by the so-called "breathing" modes localized on the redox sites, which are traditionally considered within the Piepho, Krausz and Schatz vibronic model as a source of the trapping effect. The second type includes the "intercenter" vibration, which changes the distance between the redox centers enhancing thus the degree of delocalization in the bonding orbital of the cell. The cell-cell response function as a key characteristic of the cell is evaluated in the framework of the dynamic (quantum-mechanical) solution of the two-mode vibronic problem. To elucidate the physical sense of precise quantum-mechanical results, a more imaginative semiclassical (adiabatic) picture is used. Competitive effects of the two kinds of active vibrations on the cell-cell response function are analyzed and the conditions are established under which a mixed-valence dimer can work as a functioning molecular cell in a quantum cellular automation device. One of the aims of this article was to combine the parametric approach that gives a very common description (that allows the qualitative comparison of properties in a series of compounds) with the ab initio evaluations providing numerical estimations of the parameters involved in the semiempirical approach for a real molecule. Along with the parametric approach the quantum-chemical modelling is used for investigating the cation-radical of the tetramethyleneethane molecule which was shown to belong to the class of strongly delocalized systems. It was demonstrated that an efficient control over the electronic and vibronic parameters can be achieved through the design of its derivatives through a spacer interposed between the two allyl fragments. The strongly conjugated C[double bond, length as m-dash]C spacer was shown to partially block the channel mediating electronic communication so that the molecule becomes strongly localized. The interconnection between the parametric and ab initio approaches is established.