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  • 1.
    Camisasca, Gaia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Radial distribution functions of water: Models vs experiments2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044502Article in journal (Refereed)
    Abstract [en]

    We study the temperature behavior of the first four peaks of the oxygen-oxygen radial distribution function of water, simulated by the TIP4P/2005, MB-pol, TIP5P, and SPC/E models and compare to experimental X-ray diffraction data, including a new measurement which extends down to 235 K [H. Pathak et al., J. Chem. Phys. 150, 224506 (2019)]. We find the overall best agreement using the MB-pol and TIP4P/2005 models. We observe, upon cooling, a minimum in the position of the second shell simulated with TIP4P/2005 and SPC/E potentials, located close to the temperature of maximum density. We also calculated the two-body entropy and the contributions coming from the first, second, and outer shells to this quantity. We show that, even if the main contribution comes from the first shell, the contribution of the second shell can become important at low temperature. While real water appears to be less ordered at short distance than obtained by any of the potentials, the different water potentials show more or less order compared to the experiments depending on the considered length-scale.

  • 2.
    Kim, Kyung Hwan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Mariedahl, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Katayama, Tetsuo
    Harada, Yoshihisa
    Ogasawara, Hirohito
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Temperature-Independent Nuclear Quantum Effects on the Structure of Water2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 7, article id 075502Article in journal (Refereed)
    Abstract [en]

    Nuclear quantum effects (NQEs) have a significant influence on the hydrogen bonds in water and aqueous solutions and have thus been the topic of extensive studies. However, the microscopic origin and the corresponding temperature dependence of NQEs have been elusive and still remain the subject of ongoing discussion. Previous x-ray scattering investigations indicate that NQEs on the structure of water exhibit significant temperature dependence [Phys. Rev. Lett. 94, 047801 (2005)]. Here, by performing wide-angle x-ray scattering of H2O and D2O droplets at temperatures from 275 K down to 240 K, we determine the temperature dependence of NQEs on the structure of water down to the deeply supercooled regime. The data reveal that the magnitude of NQEs on the structure of water is temperature independent, as the structure factor of D2O is similar to H2O if the temperature is shifted by a constant 5 K, valid from ambient conditions to the deeply supercooled regime. Analysis of the accelerated growth of tetrahedral structures in supercooled H2O and D2O also shows similar behavior with a clear 5 K shift. The results indicate a constant compensation between NQEs delocalizing the proton in the librational motion away from the bond and in the OH stretch vibrational modes along the bond. This is consistent with the fact that only the vibrational ground state is populated at ambient and supercooled conditions.

  • 3.
    Kim, Kyung Hwan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Mariedahl, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Lee, Jae Hyuk
    Kim, Sangsoo
    Park, Jaehyun
    Nam, Ki Hyun
    Katayama, Tetsuo
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Maxima in the thermodynamic response and correlation functions of deeply supercooled water2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 358, no 6370, p. 1589-1593Article in journal (Refereed)
    Abstract [en]

    Femtosecond x-ray laser pulses were used to probe micrometer-sized water droplets that were cooled down to 227 kelvin in vacuum. Isothermal compressibility and correlation length were extracted from x-ray scattering at the low-momentum transfer region. The temperature dependence of these thermodynamic response and correlation functions shows maxima at 229 kelvin for water and 233 kelvin for heavy water. In addition, we observed that the liquids undergo the fastest growth of tetrahedral structures at similar temperatures. These observations point to the existence of a Widom line, defined as the locus of maximum correlation length emanating from a critical point at positive pressures in the deeply supercooled regime. The difference in the maximum value of the isothermal compressibility between the two isotopes shows the importance of nuclear quantum effects.

  • 4.
    Mariedahl, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Benmore, Chris
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    X-ray studies of the transformation from high- to low-density amorphous water2019In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 377, no 2146, article id 20180164Article in journal (Refereed)
    Abstract [en]

    Here we report about the structural evolution during the conversion from high-density amorphous ices at ambient pressure to the low-density state. Using high-energy X-ray diffraction, we have monitored the transformation by following in reciprocal space the structure factor SOO(Q) and derived in real space the pair distribution function gOO(r). Heating equilibrated high-density amorphous ice (eHDA) at a fast rate (4Kmin-1), the transition to the low-density form occurs very rapidly, while domains of both high-and low-density coexist. On the other hand, the transition in the case of unannealed HDA (uHDA) and very-high-density amorphous ice is more complex and of continuous nature. The direct comparison of eHDA and uHDA indicates that the molecular structure of uHDA contains a larger amount of tetrahedral motives. The different crystallization behaviour of the derived low-density amorphous states is interpreted as emanating from increased tetrahedral coordination present in uHDA. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

  • 5.
    Mariedahl, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Benmore, Chris
    Pettersson, Lars Gunnar Moody
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Arnann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 30, p. 7616-7624Article in journal (Refereed)
    Abstract [en]

    The structure factor and oxygen-oxygen pair distribution functions of amorphous ices at liquid nitrogen temperature (T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 angstrom, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 angstrom, respectively, with high accuracy due to measurements up to a large momentum transfer of 23 angstrom(-1). Similarities in pair-distribution functions between LDA and supercooled water at 254.1 K, HDA and liquid water at 365.9 K, and VHDA and high-pressure liquid water were found up to around 8 angstrom, but beyond that at longer distances, the similarities were lost. In addition, the structure of the high-density amorphous ices was compared to high-pressure crystalline ices IV, IX, and XII, and conclusions were drawn about the local ordering.

  • 6.
    Pathak, Harshad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Palmer, J. C.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, J. A.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    The structural validity of various thermodynamical models of supercooled water2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 13, article id 134507Article in journal (Refereed)
    Abstract [en]

    The thermodynamic response functions of water exhibit an anomalous increase upon cooling that becomes strongly amplified in the deeply supercooled regime due to structural fluctuations between disordered and tetrahedral local structures. Here, we compare structural data from recent x-ray laser scattering measurements of water at 1 bar and temperatures down to 227 K with structural properties computed for several different water models using molecular dynamics simulations. Based on this comparison, we critically evaluate four different thermodynamic scenarios that have been invoked to explain the unusual behavior of water. The critical point-free model predicts small variations in the tetrahedrality with decreasing temperature, followed by a stepwise change at the liquid-liquid transition around 228 K at ambient pressure. This scenario is not consistent with the experimental data that instead show a smooth and accelerated variation in structure from 320 to 227 K. Both the singularity-free model and ice coarsening hypothesis give trends that indirectly indicate an increase in tetrahedral structure with temperature that is too weak to be consistent with experiment. A model that includes an apparent divergent point (ADP) at high positive pressure, however, predicts structural development consistent with our experimental measurements. The terminology ADP, instead of the commonly used liquid-liquid critical point, is more general in that it focuses on the growing fluctuations, whether or not they result in true criticality. Extrapolating this model beyond the experimental data, we estimate that an ADP in real water may lie around 1500 +/- 250 bars and 190 +/- 6 K.

  • 7.
    Pathak, Harshad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Temperature dependent anomalous fluctuations in water: shift of approximate to 1 kbar between experiment and classical force field simulations2019In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028Article in journal (Refereed)
    Abstract [en]

    Here we report on the temperature dependence of the anomalous behaviour of water in terms of (i) its growth in tetrahedral structures, (ii) instantaneous spatial correlations from small angle x-ray scattering (SAXS) data, (iii) estimates of thermodynamic response functions of isothermal compressibility and (iv) thermal expansion coefficient. Water's thermal expansion coefficient is estimated for the first time at supercooled conditions from liquid water's structure factor. We used previously published data from classical force-fields of TIP4P/2005 and iAMOEBA to compare experimental data with molecular dynamics simulations and observe that these force-fields underestimate water's anomalous behaviour but perform better upon increasing pressure. We demonstrate that the molecular dynamics simulations can describe better the temperature dependent anomalous behaviour of ambient pressure water if simulated at 1 kbar. The deviation in anomalous fluctuations in the simulations is not restricted to approximate to 228 K but extends all the way to ambient temperatures.

  • 8.
    Pathak, Harshad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Tsironi, Ifigeneia
    Stockholm University, Faculty of Science, Department of Physics.
    Mariedahl, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Blanco, Maria
    Huotari, Simo
    Honkimäki, Veijo
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Intermediate range O-O correlations in supercooled water down to 235 K2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 22, article id 224506Article in journal (Refereed)
    Abstract [en]

    Wide angle x-ray scattering of supercooled water down to 234.8 K was studied using high energy x rays at the European Synchrotron Radiation Facility. The oxygen-oxygen pair distribution function (PDF) was calculated from the scattering pattern out to the 5th peak at an intermolecular distance, r approximate to 11 angstrom. We observe that the 4th peak and the 5th peak in the PDF increase in height upon supercooling. We also observe that the 4th peak position (r(4)) shifts to shorter distances upon supercooling consistent with previous studies, but we see a more rapid change at the lowest temperature. The running oxygen-oxygen coordination number is calculated for 5 different temperatures, and an isosbestic point at r(iso) = 3.31 +/- 0.05 angstrom was found corresponding to a coordination number of 4.39 +/- 0.15. The comparison of the PDF of the coldest water with that of amorphous ice shows distinct differences. We propose that there are 5-member pentamer rings in low density liquid-like structures giving rise to the sharp correlations at r approximate to 9 angstrom and r approximate to 11 angstrom.

  • 9.
    Perakis, Fivos
    et al.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Lehmkühler, Felix
    Sprung, Michael
    Mariedahl, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Cavalca, Filippo
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Ricci, Alessandro
    Jain, Avni
    Massani, Bernhard
    Aubree, Flora
    Benmore, Chris J.
    Loerting, Thomas
    Grübel, Gerhard
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Diffusive dynamics during the high-to-low density transition in amorphous ice2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 31, p. 8193-8198Article in journal (Refereed)
    Abstract [en]

    Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high(HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distribution function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, arising from viscoelastic relaxation and stress release from nanometer-sized heterogeneities. Above 110 K a faster, strongly temperature-dependent component appears, with momentum transfer dependence pointing toward nanoscale diffusion. This dynamical component slows down after transition into the low-density form at 130 K, but remains diffusive. The diffusive character of both the high- and low-density forms is discussed among different interpretations and the results are most consistent with the hypothesis of a liquid-liquid transition in the ultraviscous regime.

  • 10.
    Perakis, Fivos
    et al.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Lane, Thomas J.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Lehmkühler, Felix
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Schreck, Simon
    Stockholm University, Faculty of Science, Department of Physics.
    Song, Sanghoon
    Sato, Takahiro
    Sikorski, Marcin
    Eilert, Andre
    McQueen, Trevor
    Ogasawara, Hirohito
    Nordlund, Dennis
    Roseker, Wojciech
    Koralek, Jake
    Nelson, Silke
    Hart, Philip
    Alonso-Mori, Roberto
    Feng, Yiping
    Zhu, Diling
    Robert, Aymeric
    Grübel, Gerhard
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Coherent X-rays reveal the influence of cage effects on ultrafast water dynamics2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1917Article in journal (Refereed)
    Abstract [en]

    The dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.

  • 11.
    Späh, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Mariedahl, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Lee, Jae Hyuk
    Kim, Sangsoo
    Park, Jaehyun
    Nam, Ki Hyun
    Katayama, Tetsuo
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Apparent power-law behavior of water's isothermal compressibility and correlation length upon supercooling2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 1, p. 26-31Article in journal (Refereed)
    Abstract [en]

    The isothermal compressibility and correlation length of supercooled water obtained from small-angle X-ray scattering (SAXS) were analyzed by fits based on an apparent power-law in the temperature range from 280 K down to the temperature of maximum compressibility at 229 K. Although the increase in thermodynamic response functions is not towards a critical point, it is still possible to obtain an apparent power law all the way to the maximum values with best-fit exponents of gamma = 0.40 +/- 0.01 for the isothermal compressibility and nu = 0.26 +/- 0.03 for the correlation length. The ratio between these exponents is close to a value of approximate to 0.5, as expected for a critical point, indicating the proximity of a potential second critical point. Comparison of gamma obtained from experiment with molecular dynamics simulations on the iAMOEBA water model shows that it would be located at pressures in the neighborhood of 1 kbar. The high value and sharpness of the compressibility maximum observed in the experiment are not reproduced by any of the existing classical water models, thus inviting further development of simulation models of water.

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