Car-Parrinello Research Articles

Studies on charge transfer of enalapril maleate: from solid-state to molecular dynamics.

Enalapril maleate is an antihypertensive ethyl ester pro-drug with two crystalline forms. A network of hydrogenbonds in both polymorphs plays an important role on solid-state stability, charge transfer process and degradationreactions (when exposed to high humidity, temperature and/or pH changes). Supramolecular arrangement was proposed by Hirshfeld surface using the CrystalExplorer17 software and quantum theory of atoms in molecules. The electronic structure properties were calculated using the functional hybrid M06-2X with 6-311++G** base function employing diffuse and polarization functions to improve the description of hydrogen atoms on intermolecular interactions. Also, the H+ charge transfer between enalapril and maleate molecules was performed using Car-Parrinello molecular dynamics with the Verlet algorithm. In both simulations, the temperature of the ionic system was maintained around 300 K using the Nosé-Hoover thermostat and the electronic system evolved without the use of the thermostat. This work evaluates the effect of maleate on the structural stability of enalapril maleate solid state. The electronic structural analysis points out a partially covalent character for N1-H∙∙∙O7 interaction; and the molecular dynamic showed a decentralized hydrogen on maleate driving a decomposition by charge transfer process while a centered hydrogen driving the stabilization. The charge transfer process and the mobility of the proton (H+) between enalapril and maleate molecules was demonstrated using supramolecular modeling analyses and molecular dynamics calculations.

Mechanism of Water Dissociation with an Electric Field and a Graphene Oxide Catalyst in a Bipolar Membrane

Bipolar membranes (BPMs) have recently been incorporated into energy storage devices to increase the overall battery potential and maintain a constant pH gradient by catalyzing internal H2O dissociation. In this Article, we performed a mechanistic and kinetic study of the H2O dissociation reaction on graphene oxide (GO) embedded in BPM using Car–Parrinello molecular dynamics (CPMD) and CPMD-based metadynamics methods. The synergistic effect of active sites (*OH, *C–O–C, and *C═C) on the GO catalyst and the electric field (E) strength across the GO catalyst were investigated for H2O splitting in a BPM. The results indicate the dominant activity of surface *OH sites, providing the lowest activation barrier (0.57 eV) among different sites on GO. Moreover, a higher E (>108 V/m) will significantly facilitate the dissociation reaction by polarizing the H–O bond in H2O. Our findings provide avenues for improving the BPM efficiency to achieve higher energy and power densities for next-generation energy storages.

Inter- vs. Intra-Molecular Hydrogen Bond in Complexes of Nitrophthalic Acids with Pyridine.

This study covers the analysis of isomeric forms of nitrophthalic acids with pyridine. This work dwells on the complementary experimental (X-ray, IR and Raman) and theoretical (Car-Parrinello Molecular Dynamics (CPMD) and Density Functional Theory (DFT)) studies of the obtained complexes. The conducted studies showed that steric repulsion between the nitro group in ortho-position and the carboxyl group causes significant isomeric changes. Modeling of the nitrophthalic acid-pyridine complex yielded a short strong intramolecular hydrogen bond (SSHB). The transition energy from the isomeric form with an intermolecular hydrogen bond to the isomeric form with an intramolecular hydrogen bond was estimated.

Atmospheric chemical behaviors of (CF3)2CFCN by density‐functional theory method: The relationship between electronic structure and atmosphere lifetime

Abstract(CF3)2CFCN with excellent insulation performance has been proposed to replace the traditional SF6 as a new insulating medium in power equipment. In the present study, the molecular structure and radiative efficiency (RE) of (CF3)2CFCN are calculated and compared with SF6 based on density‐functional theory (DFT) calculation. The decomposition of pure (CF3)2CFCN and the basic interactions between (CF3)2CFCN and hydroxyl radical in the constructed co‐crystal of (CF3)2CFCN‐H2O have been simulated by applying Monte‐Carlo calculation and Car–Parrinello molecular dynamics method, in order to obtain reasonable and full‐scale atmospheric dissociation processes. Then the detailed decomposition pathways are learned with DFT method of M06‐2X. The rate constants of different pathways are further applied for calculating the atmosphere lifetime of (CF3)2CFCN, to evaluate the possibility of applying it as an alternative gas of SF6 in power equipment. All the atmospheric chemical behaviors are determined by electronic structure and reflected by the decomposition pathways of (CF3)2CFCN with interacting with hydroxyl radicals. Rather than traditional hypothesizing reaction models given by the chemical intuitions, this study provides a new view angle to understand the dissociation pathways based on first‐principle molecular dynamic method, and to evaluate the atmospheric chemical behaviors of other protective gas of power equipment.

Understanding the mechanism of the sulfur mustard hydrolysis reaction on the atomistic level from experiment and first-principles simulations

After World War II, the Baltic Sea was contaminated by dumping unused sulfur mustard (SM) and other chemical warfare agents (CWAs), which now constitutes a huge environmental hazard. We use both experimental and theoretical methods to understand the reactivity of SM in water, in particular the hydrolysis, which is one of the chemical reactions leading to the neutralization of SM. Real conditions present in the Baltic Sea are represented by performing Car-Parrinello molecular dynamics simulations for sulfur mustard in explicit water solution at finite temperature. We study the relative occurrence and stability of various SM conformers in water and analyze the solute–solvent interactions, with special focus on the formation of intra- and intermolecular hydrogen bonds and their lifetime. A missing piece toward the understanding of the sulfonium cation formation and SM hydrolysis reaction is provided by obtaining the activation energy for SM decomposition in water solution from gas chromatography–mass spectrometry (GC-MS) experiments. The complex mechanism of SM hydrolysis is also studied by umbrella sampling simulations to obtain the free energy barrier for the sulfonium cation formation and to provide an atomistic view of the reaction process.

Unraveling the Nature of Hydrogen Bonds of "Proton Sponges" Based on Car-Parrinello and Metadynamics Approaches.

The nature of intra- and intermolecular non-covalent interactions was studied in four naphthalene derivatives commonly referred to as "proton sponges". Special attention was paid to an intramolecular hydrogen bond present in the protonated form of the compounds. The unsubstituted "proton sponge" served as a reference structure to study the substituent influence on the hydrogen bond (HB) properties. We selected three compounds substituted by methoxy, amino, and nitro groups. The presence of the substituents either retained the parent symmetry or rendered the compounds asymmetric. In order to reveal the non-covalent interaction properties, the Hirshfeld surface (HS) was computed for the crystal structures of the studied compounds. Next, quantum-chemical simulations were performed in vacuo and in the crystalline phase. Car-Parrinello molecular dynamics (CPMD), Path Integral Molecular Dynamics (PIMD), and metadynamics were employed to investigate the time-evolution changes of metric parameters and free energy profile in both phases. Additionally, for selected snapshots obtained from the CPMD trajectories, non-covalent interactions and electronic structure were studied. Quantum theory of atoms in molecules (QTAIM) and the Density Overlap Regions Indicator (DORI) were applied for this purpose. It was found based on Hirshfeld surfaces that, besides intramolecular hydrogen bonds, other non-covalent interactions are present and have a strong impact on the crystal structure organization. The CPMD results obtained in both phases showed frequent proton transfer phenomena. The proton was strongly delocalized in the applied time-scale and temperature, especially in the PIMD framework. The use of metadynamics allowed for tracing the free energy profiles and confirming that the hydrogen bonds present in "proton sponges" are Low-Barrier Hydrogen Bonds (LBHBs). The electronic and topological analysis quantitatively described the temperature dependence and time-evolution changes of the electronic structure. The covalency of the hydrogen bonds was estimated based on QTAIM analysis. It was found that strong hydrogen bonds show greater covalency, which is additionally determined by the proton position in the hydrogen bridge.

Vibrational spectra of human tissues: Experimental data and density functional theory calculations comparison

Biophotonics techniques enabling molecular sensing of tissues and biological samples of had been widely applied to biomedical problems. Vibrational spectroscopy technologies like Fourier-Transform Infrared (FTIR) spectroscopy is a well-reported example. However, the correct interpretation of measured vibrational spectra of macromolecules and tissues emerging from the complexity of structures is a challenge. Computer simulations can be used as a strategic method to understand interactions between specific parts of a macromolecule. Here we present two implementations of vibrational calculations based on diagonalization of Hessian matrix obtained via Density Functional Theory calculations using Car-Parrinello Molecular Dynamics (CPMD package), Born-Oppenheimer Molecular Dynamics quickstep GPW (CP2K package), and a molecular dynamics calculations based on tight binding (CP2K-TB) was also employed to obtain FTIR spectra via electric dipole correlation function. These calculations were proposed to capture vibrational pieces of information related to FTIR of the human oral mucosa. Eleven models of peptide which represents collagen type I macromolecule including confined water molecules (ranging from 0 to 8 waters), were tested. CPMD and CP2K methods presented an excellent agreement of vibrational bands positions and maximum intensity to experimental data (goodness-of-fit R2 ∼ 0.90). On the other hand, this agreement was very poor for the CP2K-TB case in spite of the correct overall relative spectral intensity with respect to experimental data. We found that the peptide model enclosing eight waters (labeled C8) in CPMD calculations presented the highest value of R2 = 0.99. The CPMD method, despite some limitations, outperformed the CP2K calculation in our case. Here we only used a collagen cutout and confined water, but it is possible to add other molecules such as proteoglycans to investigate and characterize a tissue. The short collagen mimetic peptide has implications for the conformational behavior of native collagen. The method itself can be used for other macromolecules. Furthermore, we assignment of vibrational modes in the high-wavenumber region ( > 2, 000▒cm−1) is also presented.

Quantitative and structural analysis of water association in water-lithium bromide-1,3-dimethylimidazolium chloride mixtures

In this work we report on the quantitative and structural analysis of the water association in water-lithium bromide-1,3-dimethylimidazolium chloride mixtures using multivariate curve resolution based on alternating least squares (MCR-ALS) of Near Infrared (NIR) spectra and Molecular Dynamics (MD) simulations. (NIR + MCR) methodology was used to determine the bulk water amount, as well as the mole ratio between the H2O/absorbent of the solvated structures. Measurements were performed for ternary mixtures prepared with absorbent mole fraction (LiBr + [Dmim][Cl]) from 0 to 0.5987 and the MD simulations were carried out at selected compositions within this concentration range. The results revealed the existence of three water chemical environments: bulk water in absence of solutes, bulk water coexisting with solvated water and solvated water. The comparative analysis of results with those obtained for binary mixtures (H2O + LiBr) and (H2O + [Dmim][Cl]) evidenced that the water amount that remains as bulk water in ternary solutions is higher than in binary mixtures. Classical MD simulations for five different concentrations of absorbent confirmed that water environment evolves from being essentially coordinated with other water molecules in the most diluted system, to being mainly surrounded by monoatomic ions for the most concentrated mixture. Furthermore, higher interaction between the ions appears with increasing the absorbent mole fraction, which is confirmed by Car-Parrinello MD simulations.

Structural analysis of Cu/Zeolite with controlled Si/Al ratio and the resulting thermal stability

Cu-loaded zeolite (Cu/Zeolite or Cu/CHA) has been prepared from USY (SiO2/Al2O3 =30) through hydrothermal conversion using trimethyladamantylammonium ion (TMAda) as an organic structure directing agent. Simple control over the concentration of mineralizing agent in the hydrothermal synthesis from 0.2 to 0.6 with respect to SiO2, changed the Si/Al ratio in the resulting zeolite, CHA with a decrease of overall yield. The result of 29Si NMR and 27Na spectrum of the synthesis gel and mother liquor suggested the zeolite formation through hydrothermal conversion did not occur when the monomeric Si species was increased significantly while TMAdaOH can lead to the formation of CHA similar to the synthesis of conventional silica source. Still, the textural properties and crystallographic structure of the obtained CHA have remained the same but the fraction of the strong acidity was increased significantly with the increase of the Si/Al ratio. High silica CHA shows superior hydrothermal stability in selective catalytic reduction of NOx, consistent with the result of lattice optimization using General Utility Lattice program (GULP) with the core-shell potential. Further, the results of the molecular dynamics simulation using Car-Parrinello method indicated the rapid migration of proton in CHA with a low Si/Al ratio while monovalent alkali metal ions stabilized near the double six membered rings, implying proton hopping can affect the stability of the zeolite.

Car-Parrinello molecular dynamics study of CuF, AgF, CuPF6 and AgPF6 in acetonitrile solvent and Cluster-Continuum calculation of the solvation free energy of Cu(I), Ag(I) and Li(I)

The CuF species in acetonitrile solution is a potential intermediate in copper catalyzed fluorination. In the process, different species such as Cu+, Ag+, CuF and AgF could be involved. The objective of this work is to provide relevant data on the structure of these species in solution phase, as well as the corresponding solvation thermodynamics to better understand the equilibrium for formation of CuF. To attain this goal, ab initio Car-Parrinello molecular dynamics method and cluster-continuum quasichemical approach were used. It was found that Cu+ and Ag+ ions are tetracoordinated by acetonitrile molecules, being possible to observe the release of one coordinated acetonitrile to the solution to form a tricoordinate structure, suggesting a dissociative mechanism for ligand exchange. The CuF species was found to form a predominant tricoordinate complex, with copper coordinated to two acetonitrile molecules. The AgF species have presented more labile ligand feature, with silver ion interconverting between bi- and tricoordinate structure, involving coordination to one and two acetonitrile molecules, respectively. The solvation free energy calculated for Cu+ and Ag+ are in good agreement with available experimental data. The present results indicate that CuF can be easily formed from dissolved AgF and Cu+ species in acetonitrile solution. Consequently, CuF could play an important role in copper catalyzed fluorination.

Using Car-Parrinello simulations and microscopic order descriptors to reveal two locally favored structures with distinct molecular dipole moments and dynamics in ambient liquid water

Water is essential for life and technological applications, mainly for its unique thermodynamic and dynamic properties, often anomalous or counterintuitive. These anomalies result from the hydrogen-bonds fluctuations, as evidenced by studies for supercooled water. However, it is difficult to characterize these fluctuations under ambient conditions. Here, we fill this knowledge gap thanks to the Car-Parrinello ab initio molecular dynamics (MD) simulation technique. We calculate the local structural order parameter ζ, quantifying the coordination shells separation, and find two locally-favored structures or states: High-ζ and Low-ζ. On average, High-ζ molecules have a tetrahedral arrangement, with four hydrogen bonds, and the first and the second coordination shell well separated. The Low-ζ molecules are less connected, partially merging the first and the second shells. The appearance of isosbestic points in the radial distribution functions and the collective density fluctuations at different length scales and timescales reveal that the two-state model, consistent with available experimental data for supercooled water, also holds under ambient conditions, as we confirm by analyzing the vibrational spectrum of both types of water molecules. Significant consequences of the structural differences between the two states are that High-ζ molecules have a dipole moment 6 % higher than Low-ζ. At the same time, Low-ζ structures are more disordered and with more significant angular fluctuations. These differences are also reflected in the dynamics under ambient conditions. The Low-ζ molecules decorrelate their reorientation faster than High-ζ and merge their coordination shells within 0.2 ps, while the High-ζ preserve the shell separation for longer times. Our analysis shows that first-principle calculations make predictions under ambient conditions calling for new and definitive experiments confirming the two-state model.

Accurate diffusion coefficients of the excess proton and hydroxide in water via extensive ab initio simulations with different schemes.

Despite its simple molecular formula, obtaining an accurate in silico description of water is far from straightforward. Many of its very peculiar properties are quite elusive, and in particular, obtaining good estimations of the diffusion coefficients of the solvated proton and hydroxide at a reasonable computational cost has been an unsolved challenge until now. Here, I present extensive results of several unusually long ab initio molecular dynamics (MD) simulations employing different combinations of the Born-Oppenheimer and second-generation Car-Parrinello MD propagation methods with different ensembles (NVE and NVT) and thermostats, which show that these methods together with the RPBE-D3 functional provide a very accurate estimation of the diffusion coefficients of the solvated H3O+ and OH- ions, together with an extremely accurate description of several properties of neutral water (such as the structure of the liquid and its diffusion and shear viscosity coefficients). In addition, I show that the estimations of DH3O+ and DOH- depend dramatically on the simulation length, being necessary to reach timescales in the order of hundreds of picoseconds to obtain reliable results.

Enhanced Selectivity of the Propylene Epoxidation Reaction on a Cu Monolayer Surface via Eley-Rideal Mechanism.

The aerobic oxidation of propylene to selectively achieve propylene oxide (PO) is a challenging reaction in catalysis. Therefore, an active catalyst which shows enhanced PO selectivity is extremely desired. In the present investigation, an attempt has been made to explore the catalytic activity of a mono-atomically thin two-dimensional (2D) hexagonal (HX) Cu layer for selective propylene epoxidation using molecular O2 with the aid of density functional theory calculations. The results reveal that the conversion of propylene to PO via Eley-Rideal mechanism is an exoergic and barrierless reaction on the O2 pre-adsorbed Cu monolayer. The Pauli energy component plays a decisive role for barrierless reaction whereas the electrostatic and orbital contribution governs the energetic stability of PO. Car-Parrinello molecular dynamics (CPMD) simulation reinforces the outcomes of climbing image nudged elastic band (CI-NEB) calculation. Further, the formation of oxametallacycle OMC-2 (0.47 eV) is kinetically favourable over OMC-1 (0.87 eV) and AHS (0.50 eV) on O pre-adsorbed 2D HX Cu. Interestingly, the energy barrier for the conversion of OMC-2 to PO (0.70 eV) is considerably low in comparison with the acetone formation (0.90 eV). Therefore, it is worth to mention that the 2D HX Cu surface provides a promising platform for selective propylene epoxidation.

Structure and interactions at the Mg(0001)/water interface: An ab initio study.

A molecular level understanding of metal/bulk water interface structure is key for a wide range of processes, including aqueous corrosion, which is our focus, but their buried nature makes experimental investigation difficult and we must mainly rely on simulations. We investigate the Mg(0001)/water interface using second generation Car-Parrinello molecular dynamics (MD) to gain structural information, combined with static density functional theory calculations to probe the atomic interactions and electronic structure (e.g., calculating the potential of zero charge). By performing detailed structural analyses of both metal-surface atoms and the near-surface water, we find that, among other insights: (i) water adsorption causes significant surface roughening (the planar distribution for top-layer Mg has two peaks separated by ≈0.6Å), (ii) strongly adsorbed water covers only ≈14 of available surface sites, and (iii) adsorbed water avoids clustering on the surface. Static calculations are used to gain a deeper understanding of the structuring observed in MD. For example, we use an energy decomposition analysis combined with calculated atomic charges to show that adsorbate clustering is unfavorable due to Coulombic repulsion between adsorption site surface atoms. Results are discussed in the context of previous simulations carried out on other metal/water interfaces. The largest differences for the Mg(0001)/water system appear to be the high degree of surface distortion and the minimal difference between the metal work function and metal/water potential of zero charge (at least compared to other interfaces with similar metal-water interaction strengths). The structural information, in this paper, is important for understanding aqueous Mg corrosion, as the Mg(0001)/water interface is the starting point for key reactions. Furthermore, our focus on understanding the driving forces behind this structuring leads to important insights for general metal/water interfaces.

Revealing Intra- and Intermolecular Interactions Determining Physico-Chemical Features of Selected Quinolone Carboxylic Acid Derivatives.

The intra- and intermolecular interactions of selected quinolone carboxylic acid derivatives were studied in monomers, dimers and crystals. The investigated compounds are well-recognized as medicines or as bases for further studies in drug design. We employed density functional theory (DFT) in its classical formulation to develop gas-phase and solvent reaction field (PCM) models describing geometric, energetic and electronic structure parameters for monomers and dimers. The electronic structure was investigated based on the atoms in molecules (AIM) and natural bond orbital (NBO) theories. Special attention was devoted to the intramolecular hydrogen bonds (HB) present in the investigated compounds. The characterization of energy components was performed using symmetry-adapted perturbation theory (SAPT). Finally, the time-evolution methods of Car–Parrinello molecular dynamics (CPMD) and path integral molecular dynamics (PIMD) were employed to describe the hydrogen bond dynamics as well as the spectroscopic signatures. The vibrational features of the O-H stretching were studied using Fourier transformation of the autocorrelation function of atomic velocity. The inclusion of quantum nuclear effects provided an accurate depiction of the bridged proton delocalization. The CPMD and PIMD simulations were carried out in the gas and crystalline phases. It was found that the polar environment enhances the strength of the intramolecular hydrogen bonds. The SAPT analysis revealed that the dispersive forces are decisive factors in the intermolecular interactions. In the electronic ground state, the proton-transfer phenomena are not favourable. The CPMD results showed generally that the bridged proton is localized at the donor side, with possible proton-sharing events in the solid-phase simulation of stronger hydrogen bridges. However, the PIMD enabled the quantitative estimation of the quantum effects inclusion—the proton position was moved towards the bridge midpoint, but no qualitative changes were detected. It was found that the interatomic distance between the donor and acceptor atoms was shortened and that the bridged proton was strongly delocalized.

Structural and bonding properties of small hydrocarbons inside Ca(squarate)-metal organic framework: ab-initio study

Ab−initio Molecular Dynamic (MD) and static Density Functional Theory (DFT) are used to study the structural and bonding properties of small hydrocarbon adsorbates inside Ca(squarate)−Metal Organic Framework (MOF). Car−Parrinello Molecular Dynamics (CPMD) simulations of a single−adsorbate−MOF structure are used to obtain the adsorbate most preferred site of adsorption. This site is used for further structural and bonding analyses using static DFT. Unlike many other MOFs; we found that the Ca(squarate)−MOF physisorbs and weakly binds small adsorbate molecules such as C2H2, C2H4, C2H6, and C3H8 with no observed charge transfer and minimal hybridization with the MOF orbitals. No covalent bonding is seen near the preferred site of adsorption. The calculated binding energies decreases as the H content in the adsorbate molecule increases and found to be −18.71 kJ/mol, −18.14 kJ/mol, −15.75 kJ/mol, and—4.47 kJ/mol for C2H2, C2H4, C2H6, and C3H8 molecules respectively. Density of State (DOS) and a Crystal Orbital Overlap Population (COOP) analyses show that the interactions between C and H atoms in the molecule and C and O atoms in the MOF have antibonding characteristics near the Fermi level. These antibonding states tend to destabilize the overall electronic structure of the combined adsorbate/MOF system and hence decrease the binding energies of these adsorbates inside the MOF.

Local proton hopping mechanism in imidazolium-based plastic crystal: an ab initio molecular dynamics study

Abstract Protic organic ionic plastic crystals (POIPCs) are promising solid-state proton conductor materials in anhydrous proton exchange membrane fuel cells, due to their mechanical flexibility and high ionic conductivity in the plastic crystal phase. In typical POIPCs, the ions are orientationally disordered while the centers of mass are ordered (positional order) like the crystal phase. The local disorder provides more degrees of freedom for the translational and rotational diffusion of ions, thus enhancing proton conduction either via the vehicle mechanism or the Grotthuss mechanism. Yet the local dynamics and the interactions of the cations and anions during the proton transfer process are far from being fully understood. Here, we performed Car–Parrinello molecular dynamics (CPMD) simulation on the imidazolium methanesulfate ([ImH][CH3SO3]) unit cell. By artificially creating one proton hole, we found that a proton can hop directly between the cations. Though the anion is not directly involved in proton hopping, the oxygen atom in the sulfonate group interacts with the proton and has a synergetic motion along with the proton hopping process. This indicates the structural disorder of imidazolium rings and the aid of an anion can facilitate Grotthuss-type proton hopping in imidazolium-based POIPCs.

Classical nuclear motion: Does it fail to explain reactions and spectra in certain cases?

AbstractIs a classical description of nuclear motion sufficient when describing chemical reactions and spectra? This question is interesting because many researchers use a classical description of nuclear motion in molecular dynamics simulations. The present paper investigates some phenomena that were previously attributed to nuclear quantum effects. The question is if these phenomena can be modeled with traditional Car–Parrinello molecular dynamics, that is, with a method which treats nuclear motion classically and which is widely applied to the simulation of chemical reactions and spectra. We find that for the investigated system no additional paradigm is needed for describing chemical reactions. The special reactivity observed for carbenes can be attributed to the special environment represented by a noble gas matrix and to an additional transition state that was not considered before. Also the infrared spectrum of porphycene is perfectly modeled by traditional Car–Parrinello molecular dynamics. More studies are necessary to decide to what extent classical nuclear motion can replace the quantum mechanical description.

Inside out Approach to Rotator State in Hydrogen-Bonded System-Experimental and Theoretical Cross-Examination in n-Octanol.

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from C to −15 C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from −30 C to −15 C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car–Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect’s influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated—the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Intermolecular Interactions and Spectroscopic Signatures of the Hydrogen-Bonded System-n-Octanol in Experimental and Theoretical Studies.

n-Octanol is the object of experimental and theoretical study of spectroscopic signatures and intermolecular interactions. The FTIR measurements were carried out at 293 K for n-octanol and its deuterated form. Special attention was paid to the vibrational features associated with the O-H stretching and the isotope effect. Density Functional Theory (DFT) in its classical formulations was applied to develop static models describing intermolecular hydrogen bond (HB) and isotope effect in the gas phase and using solvent reaction field reproduced by Polarizable Continuum Model (PCM). The Atoms in Molecules (AIM) theory enabled electronic structure and molecular topology study. The Symmetry-Adapted Perturbation Theory (SAPT) was used for energy decomposition in the dimers of n-octanol. Finally, time-evolution methods, namely classical molecular dynamics (MD) and Car-Parrinello Molecular Dynamics (CPMD) were employed to shed light onto dynamical nature of liquid n-octanol with emphasis put on metric and vibrational features. As a reference, CPMD gas phase results were applied. Nuclear quantum effects were included using Path Integral Molecular Dynamics (PIMD) and a posteriori method by solving vibrational Schrödinger equation. The latter applied procedure allowed to study the deuterium isotope effect.