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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Functional lipid pairs as building blocks of phase-separated membranes

Biological membranes exhibit a great deal of compositional and phase heterogeneity due to hundreds of chemically distinct components. As a result, phase separation processes in cell membranes are extremely difficult to study, especially at the molecular level. It is currently believed that the lateral membrane heterogeneity and the formation of domains, or rafts, are driven by lipid–lipid and lipid–protein interactions. Nevertheless, the underlying mechanisms regulating membrane heterogeneity remain poorly understood. In the present work, we combine inelastic X-ray scattering with molecular dynamics simulations to provide direct evidence for the existence of strongly coupled transient lipid pairs. These lipid pairs manifest themselves experimentally through optical vibrational (a.k.a. phononic) modes observed in binary (1,2-dipalmitoyl- sn -glycero-3-phosphocholine [DPPC]–cholesterol) and ternary (DPPC–1,2-dioleoyl- sn -glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-glycero-3-phosphocholine [DOPC/POPC]–cholesterol) systems. The existence of a phononic gap in these vibrational modes is a direct result of the finite size of patches formed by these lipid pairs. The observation of lipid pairs provides a spatial (subnanometer) and temporal (subnanosecond) window into the lipid–lipid interactions in complex mixtures of saturated/unsaturated lipids and cholesterol. Our findings represent a step toward understanding the lateral organization and dynamics of membrane domains using a well-validated probe with a high spatial and temporal resolution.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Skipper Charge-Coupled Device for Low-Energy-Threshold Particle Experiments above Ground

Here we present experimental results using a single-electron resolution skipper CCD running above ground level to demonstrate the potential of this technology for its use in reactor neutrino observations and other low-energy particle-interaction experiments. Operating conditions and event-selection criteria are provided to decouple most of the background rate at low energies. The majority of this background comes from interactions in the inactive silicon surrounding the active detector volume that ends up in the readout register of the sensor. Our final results are compared with other low-threshold technologies showing a good control of the background for low ionization energies down to five electron-hole pairs. This demonstrates that the skipper CCD proves to be among the best options to measure low-energy and weakly interacting particles at ground level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1975

Measurements of selected psi /3684/ branching ratios from a study of secondary lepton pairs

The measurements considered were made at the electron-positron storage ring at the Stanford Linear Accelerator Center. The apparatus used consists of two identical spectrometers mounted in a collinear configuration about the beam-interaction region. The energies of secondary electrons or positrons are measured with good resolution in large NaI(Tl) total-absorption detectors. Data accumulated without gamma-ray converters were examined for electron-positron pairs. The data taken with gamma-ray converters in place and at center-of-mass energies within 1 MeV of the resonance energy were scanned for evidence of either charged particles or converted gamma rays accompanying the detected muon pairs.

Hilger, E.↗
NASA NTRS2000

Database of non-canonical base pairs found in known RNA structures

Atomic resolution RNA structures are being published at an increasing rate. It is common to find a modest number of non-canonical base pairs in these structures in addition to the usual Watson-Crick pairs. This database summarizes the occurrence of these rare base pairs in accordance with standard nomenclature. The database, http://prion.bchs.uh.edu/, contains information such as sequence context, sugar pucker conformation, anti / syn base conformations, chemical shift, p K (a)values, melting temperature and free energy. Of the 29 anticipated pairs with two or more hydrogen bonds, 20 have been encountered to date. In addition, four unexpected pairs with two hydrogen bonds have been reported bringing the total to 24. Single hydrogen bond versions of five of the expected geometries have been encountered among the single hydrogen bond interactions. In addition, 18 different types of base triplets have been encountered, each of which involves three to six hydrogen bonds. The vast majority of the rare base pairs are antiparallel with the bases in the anti configuration relative to the ribose. The most common are the GU wobble, the Sheared GA pair, the Reverse Hoogsteen pair and the GA imino pair.

NASA Discipline Exobiology↗
NASA NTRS1990

Tidal distortions in pairs of early-type galaxies

The authors are conducting an imaging survey of pairs of elliptical galaxies which has already produced interesting results. Some pairs present a common pattern of distortion interpreted in terms of tidal effects (Davoust and Prugniel, 1988; Prugniel et al., 1989). Other examples drawn from the literature (Borne and Hoessel, 1988; Colina and Perez-Fournon, 1990) share the same morphology. New cases and lists of the characteristics of 24 such systems. The authors' pairs are drawn from a sample of binary and multiple galaxies which has in turn been extracted from the CGCG, UGC (Nilson, 1973) and VV (Vorontsov-Velyaminov, 1959) catalogues. This sample includes that of Karachentsev (1972). It contains 1800 pairs, among which 700 are S - S or mixed morphology pairs. The authors are working on the remainder to produce a sample of close physical pairs of elliptical galaxies (they also include bulge dominated SO's since the morphological discrimination from ellipticals is often ambiguous, in particular for interacting galaxies). One of the interests of this work is to provide a sample selected on purely optical criteria, at variance with other works (e.g., Valentijn and Casertano, 1988). This will allow statistical studies of non-optical properties of these pairs (in particular radio emission). The authors have so far obtained charge-coupled device (CCD) images of 125 pairs with a 2m telescope and velocities' differences of 78 pairs were obtained using the 1.93 meter telescope of Observatoire de Haute Provence and from the literature. One is an optical pair (VV 190). Eighteen of our pairs present the morphological effect described in Davoust and Prugniel (1988): the external parts of each member are stretched in opposite senses in a direction rougly perpendicular to the pair axis. The proportion of 15 plus or minus 4 percent distorted pairs confirms previous estimates. Except for a few cases involving flattened galaxies with nearly aligned major axes which deserve careful detailed analysis (Prugniel, 1989), the apparent distortions do correspond to physical distortions. We have searched the literature for isophote maps showing this effect. In the survey of radio galaxies by Colina and Perez-Fournon (1990), 7 out of 20 pairs show this characteristic distortion.

Prugniel, Philippe↗
DOE OSTI2022

Search for charged-lepton flavor violation in top quark production and decay in pp collisions at $ \sqrt{s} $ = 13 TeV

Results are presented from a search for charged-lepton flavor violating (CLFV) interactions in top quark production and decay in pp collisions at a center-of-mass energy of 13 TeV. The events are required to contain one oppositely charged electron-muon pair in the final state, along with at least one jet identified as originating from a bottom quark. The data correspond to an integrated luminosity of 138 fb$^{-1}$, collected by the CMS experiment at the LHC. This analysis includes both the production (q → eμt) and decay (t → eμq) modes of the top quark through CLFV interactions, with q referring to a u or c quark. These interactions are parametrized using an effective field theory approach. With no significant excess over the standard model expectation, the results are interpreted in terms of vector-, scalar-, and tensor-like CLFV four-fermion effective interactions. Finally, observed exclusion limits are set at 95% confidence levels on the respective branching fractions of a top quark to an eμ pair and an up (charm) quark of 0.13 × 10$^{-6}$ (1.31 × 10$^{-6}$), 0.07 × 10$^{-6}$ (0.89 × 10$^{-6}$), and 0.25 × 10$^{-6}$ (2.59 × 10$^{-6}$) for vector, scalar, and tensor CLFV interactions, respectively.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Pauling bond strength, bond length and electron density distribution

A power law regression equation, = 1.46(<ρ(rc)>/r)-0.19, connecting the average experimental bond lengths, , with the average accumulation of the electron density at the bond critical point, <ρ(rc)>, between bonded metal M and oxygen atoms, determined at ambient conditions for oxide crystals, where r is the row number of the M atom, is similar to the regression equation R(M-O) = 1.39(ρ(rc)/r)-0.21 determined for three perovskite crystals for pressures as high as 80 GPa. The two equations are also comparable with those, = 1.43( /r)-0.21, determined for a large number of oxide crystals at ambient conditions and = 1.39( /r)-0.22, determined for geometry optimized hydroxyacid molecules, that connect the bond lengths to the average Pauling electrostatic bond strength, , for the M-O bonded interactions. On the basis of the correspondence between the two sets of equations connecting ρ(rc) and the Pauling bond strength s with bond length, it appears that Pauling’s simple definition of bond strength closely mimics the accumulation of the electron density between bonded pairs of atoms. The similarity of the expressions for the crystals and molecules is compelling evidence that the M-O bonded interactions for the crystals and molecules 2 containing the same bonded interactions are comparable. Similar expressions, connecting bond lengths and bond strength, have also been found to hold for fluoride, nitride and sulfide molecules and crystals. The Brown-Shannon bond valence, σ, power law expression σ = [R1/(R(M-O)]N that has found wide use in crystal chemistry, is shown to be connected to a more universal expression determined for oxides and the perovskites, <ρ(rc)> = r[(1.41)/ ]4.76, demonstrating that the bond valence for a bonded interaction is likewise closely connected to the accumulation of the electron density between the bonded atoms. Unlike the Brown-Shannon expression, it is universal in that it holds for the M-O bonded interactions for a relatively wide range of M atoms of the periodic table. The power law equation determined for the oxide crystals at ambient conditions is similar to the power law expression <ρ(rc)> = r[1.46/ ]5.26 determined for the perovskites at pressures as high as 80 GPa, indicating that the intrinsic connection between R(M-O) and ρ(rc) that holds at ambient conditions also holds, to a first approximation, at high pressures.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

The structure-reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0\hBaO\30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in the initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (\4 ML), BaO clusters (\1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)2 forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)2 phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)2 phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)2 are identical, i.e., both of these phases can completely be converted to Ba(NO3)2. In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these ‘‘carbonated’’ BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(\1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)2 was also substantiated in experiments where Ba(NO3)2/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition. We gratefully acknowledge the US Department of Energy (DOE), Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national user facility sponsored by the DOE Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle under contract number DE-AC05-76RL01830.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Simulations of relativistic quantum plasmas using real-time lattice scalar QED

Real-time lattice quantum electrodynamics (QED) provides a unique tool for simulating plasmas in the strong-field regime, where collective plasma scales are not well separated from relativistic-quantum scales. As a toy model, we study scalar QED, which describes self-consistent interactions between charged bosons and electromagnetic fields. To solve this model on a computer, we first discretize the scalar-QED action on a lattice, in a way that respects geometric structures of exterior calculus and U(1)-gauge symmetry. The lattice scalar QED can then be solved, in the classical-statistics regime, by advancing an ensemble of statistically equivalent initial conditions in time, using classical field equations obtained by extremizing the discrete action. To demonstrate the capability of our numerical scheme, we apply it to two example problems. The first example is the propagation of linear waves, where we recover analytic wave dispersion relations using numerical spectrum. The second example is an intense laser interacting with a one-dimensional plasma slab, where we demonstrate natural transition from wakefield acceleration to pair production when the wave amplitude exceeds the Schwinger threshold. Our real-time lattice scheme is fully explicit and respects local conservation laws, making it reliable for long-time dynamics. The algorithm is readily parallelized using domain decomposition, and the ensemble may also be computed using quantum parallelism in the future.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Stellar kinematics of elliptical galaxies in pairs

In both galaxy pairs Arp 166 and 3C 278 the authors find radially increasing velocity dispersions indicating a perturbed, non-equilibrium state of the galaxies after the tidal interaction. In all galaxies, the increase is most pronounced in the regions which correspond to the centers of the outer isophotes. The authors suggest a scenario in which the galaxies are strongly decelerated on their orbits during the encounter. The deceleration depends on the radial position in the perturbed galaxy and vanishes in the center of the perturbed galaxy (Spitzer, 1958). In addition, the crossing time of the stars near the center is very short, implying that the tidal perturbations can be averaged over several orbital periods (e.g., Binney and Tremaine, 1987). In consequence, the central parts are not affected by the tidal interaction while the outer parts are strongly decelerated. This leads to a displacement of the central parts of the galaxies with respect to their envelopes in an anti-symmetrical way for the two components of each galaxy pair. The motions of the central parts subsequently are opposed by dynamical friction with the surrounding envelopes. Due to dynamical friction, the density of the stars increases in the wakes of the moving central parts (Mulder, 1983). The overdensity of stars in the wakes of the moving central parts efficiently decelerates the motions of the central parts. The reaction of the stars in the overdensity regions leads to an increase of the velocity dispersion mainly along the orbits of the moving central parts. The presented observations, especially the asymmetrical luminosity profiles and the radially increasing velocity dispersions support consistently the above scenario of tidal interaction between galaxies. Further spectroscopic observations are necessary in order to investigate the degree of anisotropy in the kinematically perturbed regions.

Madejsky, Rainer↗
DOE OSTI2016

Aromatic-Aromatic Interactions in Biological System: Structure Activity Relationships

While, intramolecular hydrogen bonds have attracted the greatest attention in studies of peptide conformations, the recognition that several other weakly polar interactions may be important determinants of folded structure has been growing. Burley and Petsko provided a comprehensive overview of the importance of weakly polar interactions, in shaping protein structures. The interactions between aromatic rings, which are spatially approximate, have attracted special attention. A survey of the proximal aromatic residue pairs in proteins, allowed Burley and Petsko to suggest that, “phenyl ring centroids are separated by a preferential distance of between 4.5 and 7 Å, and dihedral angles approximately 90° are most common”.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ion transport and structural dynamics in homologous ammonium and phosphonium-based room temperature ionic liquids

Charge transport and structural dynamics in a homologous pair of ammonium and phosphonium based room temperature ionic liquids (ILs) have been characterized over a wide temperature range using broadband dielectric spectroscopy and quasi-elastic light scattering spectroscopy. We have found that the ionic conductivity of the phosphonium based IL is significantly enhanced relative to the ammonium homolog, and this increase is primarily a result of a lower glass transition temperature and higher ion mobility. Additionally, these ILs exhibit pronounced secondary relaxations which are strongly influenced by the atomic identity of the cation charge center. While the secondary relaxation in the phosphonium IL has the expected Arrhenius temperature dependence characteristic of local beta relaxations, the corresponding relaxation process in the ammonium IL was found to exhibit a mildly non-Arrhenius temperature dependence in the measured temperature range—indicative of molecular cooperativity. These differences in both local and long-range molecular dynamics are a direct reflection of the subtly different inter-ionic interactions and mesoscale structures found in these homologous ILs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structure of mouse protocadherin 15 of the stereocilia tip link in complex with LHFPL5

Hearing and balance involve the transduction of mechanical stimuli into electrical signals by deflection of bundles of stereocilia linked together by protocadherin 15 (PCDH15) and cadherin 23 ‘tip links’. PCDH15 transduces tip link tension into opening of a mechano-electrical transduction (MET) ion channel. PCDH15 also interacts with LHFPL5, a candidate subunit of the MET channel. Here we illuminate the PCDH15-LHFPL5 structure, showing how the complex is composed of PCDH15 and LHFPL5 subunit pairs related by a 2-fold axis. The extracellular cadherin domains define a mobile tether coupled to a rigid, 2-fold symmetric ‘collar’ proximal to the membrane bilayer. LHFPL5 forms extensive interactions with the PCDH15 transmembrane helices and stabilizes the overall PCDH15-LHFPL5 assembly. Our studies illuminate the architecture of the PCDH15-LHFPL5 complex, localize mutations associated with deafness, and shed new light on how forces in the PCDH15 tether may be transduced into the stereocilia membrane.

Ge, Jingpeng↗
DOE OSTI2026

Pressure‐Induced Structural and Magnetic Evolution in Layered Antiferromagnet YbMn 2 Sb 2

Electronic states under pressure exhibit unconventional spin and charge dynamics that provide a powerful route to uncover exotic phases in quantum materials. Here, we present the structural, magnetic, and electronic evolution of YbMn 2 Sb 2 under pressure. Single-crystal X-ray diffraction reveals a pressure-induced structural transition from the space group trigonal P$\overline{3}$m1 to the monoclinic P2 1 /m phase near 3.5 GPa, which remains stable up to 10 GPa. Magnetization measurements display an anomalously weak net magnetic moment and the absence of Curie–Weiss behavior up to 400 K, suggesting the formation of short-range Mn moment pairs that cancel macroscopically and subsequently evolve into long-range order upon cooling. Temperature-dependent resistivity shows semiconducting behavior with a transition at ∼119 K at ambient pressure, while pressure induces a dramatic suppression of resistance and the emergence of metallic-like temperature dependence, stabilized beyond 5 GPa. This pressure-driven semiconductor-metal transition is consistent with our density functional theory calculations, confirming the closing of the band gap under compression. Neutron diffraction under pressure identifies an incommensurate magnetic structure with antiparallel correlations between paired spins. Together, these results demonstrate how pressure-driven structural tuning and competing exchange interactions stabilize unconventional magnetic states in this low-dimensional magnetic semiconductor.

antiferromagnetic semiconductor↗
DOE OSTI2026

Probing the flavour structure of dimension-6 EFT operators in multilepton final states in proton-proton collisions at $\sqrt{s}=13$ TeV

An analysis of the flavour structure of dimension-6 effective field theory (EFT) operators in multilepton final states is presented, focusing on the interactions of quarks with Z bosons. For the first time, the flavour structure of these operators is disentangled by simultaneously probing the interactions with different quark generations. The analysis targets the associated production of a top quark pair and a Z boson, as well as diboson processes in final states with at least three leptons, which can be electrons or muons. The data were recorded by the CMS experiment in the years 2016–2018 in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb −1 . Consistency with the standard model of particle physics is observed and limits are set on the selected Wilson coefficients, split into couplings to light- and heavy-quark generations.

Flavour Physics↗
DOE OSTI2023

Ion Solvation-Driven Liquid–Liquid Phase Separation in Divalent Electrolytes with Miscible Organic Solvents

Liquid–liquid phase separation (LLPS) is a common phenomenon, but LLPS of electrolytes prepared in miscible organic solvents is rarely documented. Here we report four cases of LLPS that occur in MgTFSI 2 or ZnTFSI 2 electrolytes in mixed organic solvents. The conditions for the formation of this LLPS share four common features: cations with high charge density; bulky anions with low charge density; a strongly coordinating solvent with high compressibility; and a relatively weak coordinating solvent with low relative permittivity and high mobility. With these conditions, the cations tend to draw the strongly coordinating solvents together to form a densely-packed, energetically-favorable ion solvation region, while the cosolvents with low relative permittivity tend to repel ions to form an ion-depleted dilute phase. Furthermore, in the dilute upper layer with more than 300 solvent molecules per cation, ion pairs and large ion aggregates are clearly evidenced, due to the incomplete screening of electrostatic interactions by the weaker cosolvent. This LLPS driven by ion solvation may be more common in multivalent electrolytes and is a design consideration with mixed solvents that should not be overlooked.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ab initio pressure-dependent reaction kinetics of methyl propanoate radicals

The unimolecular dissociation and isomerization kinetics of the three methyl propanoate (MP) radicals, CH 3 CH 2 C(=O)O$\dot{C}$H 2 (MP-m), CH 3 $\dot{C}$HC(=O)OCH 3 (MP-α), and $\dot{C}$H 2 CH 2 C(=O)OCH 3 (MP-β), are theoretically investigated using high-level ab initio methods and the Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Stationary-point energies are obtained using the coupled cluster singles and doubles with perturbative triples correction (CCSD(T)), multi-reference singles and doubles configuration interaction (MRSDCI) with the Davidson-Silver (DS) correction, and multi-reference averaged coupled pair functional (MRACPF2) theories. The isomerization barriers between the three radicals are predicted to be generally lower than the corresponding bond dissociation channels, leading to a strongly coupled reaction system in subsequent kinetics studies. The phenomenological temperature- and pressure-dependent rate coefficients are computed using the RRKM/ME theory over a temperature range of 500 to 2000 K and at a pressure range of 0.01 atm to the high-pressure limit, which are then fitted to modified Arrhenius expressions. The β-scission rate coefficients of MP-α to CH 3 CHC(=O) and CH 3 $\dot{O}$ are predicted to be the smallest because of its highest activation energy among all studied unimolecular reactions channels. Analysis of branching fractions shows that both MP-m and MP-α radicals mainly decompose to the bimolecular products CH 3 CH 2 $\dot{C}$(=O) and H 2 CO, whereas the MP-β radical primarily decomposes via cleavage of a C–C bond to form C 2 H 4 and CH 3 O$\dot{C}$(=O). The isomerization channels dominate at low temperatures, the branching fractions of which decrease with increasing temperature and become very minor at about 2000 K. Our accurate rate coefficients and branching fractions help to illuminate the unique combustion properties of MP.

09 BIOMASS FUELS↗
DOE OSTI2015

Fluid-solid transition in simple systems using density functional theory

A free energy functional for a crystal which contains both the symmetry-conserved and symmetry-broken parts of the direct pair correlation function has been used to investigate the fluid-solid transition in systems interacting via purely repulsive Weeks-Chandler-Anderson Lennard–Jones potential and the full Lennard–Jones potential. The results found for freezing parameters for the fluid-face centred cubic crystal transition are in very good agreement with simulation results. It is shown that although the contribution made by the symmetry broken part to the grand thermodynamic potential at the freezing point is small compared to that of the symmetry conserving part, its role is crucial in stabilizing the crystalline structure and on values of the freezing parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗