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Calculated densities for liquid bulk water. The arrows indicate the temperature of maximum density (TMD) at 315.64 K and 318.74 K for H2O and D2O, respectively.
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Ab initio calculations on molecular clusters and a quantum statistical model are used to probe the structure of liquid water and its anomalies. Characteristic temperature dependent mixtures of ring and three-dimensional, voluminous water clusters provide the famous density maximum. The mixture model also reproduces the shift of the density maximum...
Contexts in source publication
Context 1
... the (H 2 O) 17 represents the high-volume structure, the density starts to decrease going through a maximum at low temperatures (Figure 4). Thus a simple mixture model is capable to reproduce waters's most famous anomaly, the temperature of maximum density (TMD). ...
Context 2
... the initial frequency calculation for each protonated cluster is followed by a second thermochemistry analysis using a different selection of isotopes. In Figure 4 it is shown that upon deuteration, the shift of the TMD to higher temperatures is modeled correctly. However, the calculated shift of about 3 K is only half of the shift measured for physical water ( % 7 K). ...
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Citations
... These labile clusters agglomerate by sharing faces on one side of the interface until they reach a critical size for hydrate growth. This assumption is supported by Ludwig [125] who probed the structure of the water phase from ab initio calculations. The results turned out that it is very like to have ring structures in the water phase besides the tetrahedrally coordinated water molecules. ...
Gas hydrates are ice-like crystalline compounds made of water cavities that retain various types of guest molecules. Natural gas hydrates are CH4-rich but also contain higher hydrocarbons as well as CO2, H2S, etc. They are highly dependent of local pressure and temperature conditions. Considering the high energy content, natural gas hydrates are artificially dissociated for the production of methane gas. Besides, they may also dissociate in response to global warming. It is therefore crucial to investigate the hydrate nucleation and growth process at a molecular level. The understanding of how guest molecules in the hydrate cavities respond to warming climate or gas injection is also of great importance. This thesis is concerned with a systematic investigation of simple and mixed gas hydrates at conditions relevant to the natural hydrate reservoir in Qilian Mountain permafrost, China. A high-pressure cell that integrated into the confocal Raman spectroscopy ensured a precise and continuous characterization of the hydrate phase during formation/dissociation/transformation processes with a high special and spectral resolution. By applying laboratory experiments, the formation of mixed gas hydrates containing other hydrocarbons besides methane was simulated in consideration of the effects from gas supply conditions and sediments. The results revealed a preferential enclathration of different guest molecules in hydrate cavities and further refute the common hypothesis of the coexistence of hydrate phases due to a changing feed gas phase. However, the presence of specific minerals and organic compounds in sediments may have significant impacts on the coexisting solid phases. With regard to the dissociation, the formation damage caused by fines mobilization and migration during hydrate decomposition was reported for the first time, illustrating the complex interactions between fine grains and hydrate particles. Gas hydrates, starting from simple CH4 hydrates to binary CH4—C3H8 hydrates and multi-component mixed hydrates were decomposed by thermal stimulation mimicking global warming. The mechanisms of guest substitution in hydrate structures were studied through the experimental data obtained from CH4—CO2, CH4—mixed gas hydrates and mixed gas hydrates—CO2 systems. For the first time, a second transformation behavior was documented during the transformation process from CH4 hydrates to CO2-rich mixed hydrates. Most of the crystals grew or maintained when exposed to CO2 gas while some others decreased in sizes and even disappeared over time. The highlight of the two last experimental simulations was to visualize and characterize the hydrate crystals which were at different structural transition stages. These experimental simulations enhanced our knowledge about the mixed gas hydrates in natural reservoirs and improved our capability to assess the response to global warming.
... These labile clusters agglomerate by sharing faces until they reach a critical size for hydrate growth. The assumption is also supported by other studies where the existence of water cavities arranged in a pentagonal dodecahedron [36] and ring structures [37] were postulated. ...
Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed.
... A convenient method focuses on the structure change of water with respect to the structure of crystalline ice [12]. In bulk liquid water, each water molecule forms up to approximated four tetrahedrally directed hydrogen bonds with neighboring water molecules [13,14]. Such water clusters give liquid water a heterogeneous varying character with different physical and environmental conditions. ...
... The armchair CNTs with various size from (6, 6), (7,7), (8,8), (9,9), (10,10), (14,14), (20,20), and (40,40) were constructed by visual molecular dynamics (VMD) tool [33]. The diameters of various sized CNTs are listed in Table 1. ...
... The armchair CNTs with various size from (6, 6), (7,7), (8,8), (9,9), (10,10), (14,14), (20,20), and (40,40) were constructed by visual molecular dynamics (VMD) tool [33]. The diameters of various sized CNTs are listed in Table 1. ...
Various order parameters have been suggested to characterize the local structure of liquid water in bulk. Characterization the local structure of water molecules in the confined systems by various order parameters is important but still unclear. In this work, a series of popular order parameters are used to analyze the local structure of water molecules in carbon nanotubes (CNTs) by molecular dynamics simulation. Based on the value of order parameters, the different structures of water molecules in CNTs and in bulk were discussed. The orientational tetrahedral order (q) and translational tetrahedral order (Sk) are much better than local structure index (LSI) to describe the local structure of water in CNTs. We also demonstrated that the local structure of water molecules in the CNT(40,40) is almost the same with that in bulk. The findings could give us a guideline to investigate the water molecules in confined system.
... Authoritative reviews on the advancement in this field have focused on the following issues from various perspectives: from water structures [51][52][53], molecular clusters [54][55][56][57], ice The molecule is electrically neutral, thus qM = −(2qH + qO), and qH, qO, lOM, OO , and εOO are independent parameters to be determined, where OO and εOO are the L-J potential parameters for the O O interaction (reprinted with permission from [87]). (b) The 'double symmetrical potential well' model indicates that the H + proton is frustrated in the two identical sites between adjacent oxygen atoms. ...
... Reprinted with permission from [89]. nucleation and growth [22,58], ice melting [59], slipperiness and friction of ice [60], to the behavior of water ice subjected to positive [61,62] and negative pressure [54,63]. Reviews have also covered topics on water surface charge and polarization [64,65], surface photoelectron emission [66,67], phonon relaxation [24,68], water adsorption onto inorganic surfaces [69][70][71][72][73], and ion effects on water properties and structures [74], among other topics. ...
Introduction of the principles of the asymmetrical, short-range O:H-O coupled oscillater pair and the basic rule for water ice, which reconciles the structure and anomalies of water ice.
... Authoritative reviews on the advancement in this field have focused on the following issues from various perspectives: from water structures [51][52][53], molecular clusters [54][55][56][57], ice The molecule is electrically neutral, thus qM = −(2qH + qO), and qH, qO, lOM, OO , and εOO are independent parameters to be determined, where OO and εOO are the L-J potential parameters for the O O interaction (reprinted with permission from [87]). (b) The 'double symmetrical potential well' model indicates that the H + proton is frustrated in the two identical sites between adjacent oxygen atoms. ...
... Reprinted with permission from [89]. nucleation and growth [22,58], ice melting [59], slipperiness and friction of ice [60], to the behavior of water ice subjected to positive [61,62] and negative pressure [54,63]. Reviews have also covered topics on water surface charge and polarization [64,65], surface photoelectron emission [66,67], phonon relaxation [24,68], water adsorption onto inorganic surfaces [69][70][71][72][73], and ion effects on water properties and structures [74], among other topics. ...
As the basic structure element, hydrogen bond (O:H–O) is universal to all phases of water and ice irrespective geometric configuration or fluctuation order. The O:H–O bond integrates the asymmetric, coupled, short-range intermolecular and intramolecular interactions, whose segmental length and energy respond to stimulations sensitively in a “mater-slave” manner. If one segment shortens and turns to be stiffer, the other will expand and become softer. The O:H nonbond always relaxes more than the H–O bond in length. Such a manner of segmental cooperative relaxation and the associated polarization and bond angle relaxation discriminates ice and water from other substance in responding to stimuli of chemical, electrical, mechanical, thermal, and undercoordination effect, which reconcile almost all detectable properties of water and ice.
... Authoritative reviews on the advancement in this field have focused on the following issues from various perspectives: from water structures [51][52][53], molecular clusters [54][55][56][57], ice The molecule is electrically neutral, thus qM = −(2qH + qO), and qH, qO, lOM, OO , and εOO are independent parameters to be determined, where OO and εOO are the L-J potential parameters for the O O interaction (reprinted with permission from [87]). (b) The 'double symmetrical potential well' model indicates that the H + proton is frustrated in the two identical sites between adjacent oxygen atoms. ...
... Reprinted with permission from [89]. nucleation and growth [22,58], ice melting [59], slipperiness and friction of ice [60], to the behavior of water ice subjected to positive [61,62] and negative pressure [54,63]. Reviews have also covered topics on water surface charge and polarization [64,65], surface photoelectron emission [66,67], phonon relaxation [24,68], water adsorption onto inorganic surfaces [69][70][71][72][73], and ion effects on water properties and structures [74], among other topics. ...
The geometry structure, mass density ρ(g/cm3), the size (dH) and separation (dOO = dL + dH) of molecules packed in water and ice are closely correlated, which reconciles: (i) the dx symmetrization in compressed ice, (ii) the dOO relaxation of cooling water and ice and, (iii) the dOO expansion between undercoordinated molecules. With any one of the dOO, the density ρ, the dL, and the dH, as a known input, one can resolve the rest using this solution that is probing conditions or methods independent. Consistency between predictions and observations clarified that: (i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with high fluctuation, (ii) the supersolid phase (strongly polarized and much less dense) exists only in regions consisting undercoordinated molecules and, (iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H–O bond.
... 56 at least once in order to capture the fundamental physics of the system. Since pure water has already been extensively studied using the QCE method, [56][57][58][59][60][61][62][63][64][65][66][67][68] we chose a set of clusters that was found to be important in those earlier studies. It consists of the monomer (w1), the dimer (w2), two ring structures (w5, w6), a cube (w8) and a bicyclic cluster (w9), which we call spiro cluster because of its similarity to organic spiro compounds. ...
The established quantum cluster equilibrium (QCE) approach is refined and applied to N-methylformamide (NMF) and its aqueous solution. The QCE method is split into two iterative cycles: one which converges to the liquid phase solution of the QCE equations and another which yields the gas phase. By comparing Gibbs energies, the thermodynamically stable phase at a given temperature and pressure is then chosen. The new methodology avoids metastable solutions and allows a different treatment of the mean-field interactions within the gas and liquid phases. These changes are of crucial importance for the treatment of binary mixtures. For the first time in a QCE study, the cis-trans-isomerism of a species (NMF) is explicitly considered. Cluster geometries and frequencies are calculated using density functional theory (DFT) and complementary coupled cluster single point energies are used to benchmark the DFT results. Independent of the selected quantum-chemical method, a large set of clusters is required for an accurate thermodynamic description of the binary mixture. The liquid phase of neat NMF is found to be dominated by the cyclic trans-NMF pentamer, which can be interpreted as a linear trimer that is stabilized by explicit solvation of two further NMF molecules. This cluster reflects the known hydrogen bond network preferences of neat NMF.
... 21 In addition to methanol clusters those of higher primary alcohols (up to n-hexanol) were treated by Golub et al. 19 A powerful tool for the description and theoretical modelling of structure and properties of liquids is the quantum cluster equilibrium (QCE) theory 22 which is based on quantum chemically calculated cluster/molecular properties and the application of statistical thermodynamics. So far this procedure almost exclusively has been applied to neat liquids, like water, [23][24][25][26][27][28][29][30][31][32][33][34] methanol, 28,35-38 ethanol, 28,38-41 propan-1-ol, 38 butan-1-ol, 38 benzyl alcohol, 39 2,2-dimethyl-3-ethyl-3-pentanol, 39,42 formic acid, 43,44 liquid ammonia, 27,45,46 phosphine, 27 hydrogen sulfide, 27 N-methylacetamide, [47][48][49] liquid sulfur, 50 and liquid hydrogenfluoride. 34,[51][52][53] Recently, in addition to the static thermodynamic description by the QCE model, the kinetics of the hydrogen bond formation and proton transfer in water clusters has been studied by Weinhold. ...
Density functional theory (B3LYP-D3, M06-2X) has been used to calculate the structures, interaction energies and vibrational frequencies of a set of 93 methanol-water clusters of different type (cubic, ring, spiro, lasso, bicyclic), size and composition. These interaction energies have been used within the framework of the Quantum Cluster Equilibrium Theory (QCE) to calculate cluster populations as well as thermodynamic properties of binary methanol-water mixtures spanning the whole range from pure water to pure methanol. The necessary parameters amf and bxv of the QCE model were obtained by fitting to experimental isobars of MeOH-H2O mixtures with different MeOH content. The cubic and spiro motifs dominate the distribution of methanol-water clusters in the mixtures with a maximum of mixed clusters at x(MeOH) = 0.365. Reasonable agreement with experimental data as well as earlier molecular dynamics simulations was found for excess enthalpies H(E), entropies S(E) as well as Gibbs free energies of mixing G(E). In contrast, heat capacities Cp and C showed only poor agreement with experimental data.
... Authoritative reviews on the advancement in this field have focused on the following issues from various perspectives: from water structures [51][52][53], molecular clusters [54][55][56][57], ice The molecule is electrically neutral, thus qM = −(2qH + qO), and qH, qO, lOM, OO , and εOO are independent parameters to be determined, where OO and εOO are the L-J potential parameters for the O O interaction (reprinted with permission from [87]). (b) The 'double symmetrical potential well' model indicates that the H + proton is frustrated in the two identical sites between adjacent oxygen atoms. ...
... Reprinted with permission from [89]. nucleation and growth [22,58], ice melting [59], slipperiness and friction of ice [60], to the behavior of water ice subjected to positive [61,62] and negative pressure [54,63]. Reviews have also covered topics on water surface charge and polarization [64,65], surface photoelectron emission [66,67], phonon relaxation [24,68], water adsorption onto inorganic surfaces [69][70][71][72][73], and ion effects on water properties and structures [74], among other topics. ...
An extended tetrahedron unifies the length scale, geometry, and density of water ice.•O:H–O bond cooperative relaxation stems anomalies of water and ice.•Water prefers 4-coordinated mono-phase with a supersolid skin unless at nanoscale.•An elastic, hydrophobic and less dense skin slipperizes ice and toughens water skin.•H-bond memory and skin supersolidity resolve Mpemba effect - hot water freezes faster.
... Authoritative reviews have been documented in the literature on the understanding of water structures 43-45 , phonon relaxation 17,46 , surface polarization 47 , water clusters [48][49][50][51] , water adsorption to metals or other inorganic surfaces [52][53][54][55][56] , ion effects on water structure 57 , water surface charging 58 , ice surface melting 59 , slippery and friction of ice 60 , surface photoelectron emission 61,62 , and water under positive 63,64 and negative pressure 48,65 , etc., from various perspectives. Techniques have been developed for water surface and interface studies 66,67 such as the sum frequency generation (SFG) 47,68 , microjets photoelectron emission 69 , glancing angle Raman spectroscopy 70,71 , etc. ...
... Authoritative reviews have been documented in the literature on the understanding of water structures 43-45 , phonon relaxation 17,46 , surface polarization 47 , water clusters [48][49][50][51] , water adsorption to metals or other inorganic surfaces [52][53][54][55][56] , ion effects on water structure 57 , water surface charging 58 , ice surface melting 59 , slippery and friction of ice 60 , surface photoelectron emission 61,62 , and water under positive 63,64 and negative pressure 48,65 , etc., from various perspectives. Techniques have been developed for water surface and interface studies 66,67 such as the sum frequency generation (SFG) 47,68 , microjets photoelectron emission 69 , glancing angle Raman spectroscopy 70,71 , etc. ...
Hydrogen-bond forms a pair of asymmetric, coupled, H-bridged oscillators with
ultra-short-range interactions and memory. hydrogen bond cooperative relaxation
and the associated binding electron entrapment and nonbonding electron
polarization discriminate water and ice from other usual materials in the
physical anomalies.
As a strongly correlated fluctuating system, water prefers the statistically
mean of tetrahedrally-coordinated structure with a supersolid skin that is
elastic, polarized, ice like, hydrophobic, with 3/4 density.
