Molecular dynamics simulations of isothermal reactions in Al/Ni nanolaminates.

Molecular dynamics simulations of reactions in Al/Ni layered systems have been carried out under isothermal conditions for a wide range of temperatures and several system sizes. An embedded atom method potential, known to reasonably reproduce the phase behavior of Al/Ni, was employed. Simulations revealed reaction mechanisms involving an initial fast process and much slower more complex longer-time reactions. The initial reaction process consists of diffusion of Ni from the pure solid Ni phase into the molten Al phase, resulting in the formation of an Al-rich Al/Ni liquid. The initial reaction ends when the Al/Ni liquid becomes saturated in Ni and solid Al/Ni phases begin to form at the interfaces between the pure solid Ni phase and the Al/Ni liquid. The growth of these solid phases is intrinsically slow compared to the formation of the liquid and is further slowed by the need for Ni to diffuse through the growing interfacial Al/Ni solid phases. Analysis of the initial Al/Ni liquid forming process indicates Fickian behavior with the Ni diffusion coefficient exhibiting Arrhenius temperature dependence. The longer-time slow reaction process(es) resulting in the growth of Al/Ni solid phases do not lend themselves to detailed numerical analysis because of the complex dependence of the Ni transport on the detailed nature of the interfacial layers.

Abdominal lean muscle is associated with lower mortality among kidney waitlist candidates.

Morphometric assessments, such as muscle density and body fat distribution, have emerged as strong predictors of cardiovascular risk and postoperative morbidity and mortality. To date, no study has examined morphometric mortality risk prediction among kidney transplant (KT) candidates. KT candidates, waitlisted 2008-2009, were identified (n=96) and followed to the earliest of transplant, death, or administrative end of study. Morphometric measures, including abdominal adipose tissue, paraspinous and psoas muscle composition, and aortic calcification, were measured from CTs. Risk of waitlist mortality was examined using Cox proportional hazard regression. On adjusted analyses, radiologic measures remained independently and significantly associated with lower waitlist mortality; the addition of radiologic measures significantly improved model predictive ability over models containing traditional risk factors alone (net reclassification index: 0.56, 95% CI: 0.31-0.75). Higher psoas muscle attenuation (indicative of leaner muscle) was associated with decreased risk of death (aHR: 0.93, 95% CI: 0.91-0.96, P<.001), and for each unit increase in lean paraspinous volume, there was an associated 2% decreased risk for death (aHR: 0.98, 95% CI: 0.96-0.99, P=.03). Radiologic measures of lean muscle mass, such as psoas muscle attenuation and paraspinous lean volume, may improve waitlist mortality risk prediction and candidate selection.

Thermophysical properties of energetic ionic liquids/nitric acid mixtures: insights from molecular dynamics simulations.

Molecular dynamics (MD) simulations of mixtures of the room temperature ionic liquids (ILs) 1-butyl-4-methyl imidazolium [BMIM]/dicyanoamide [DCA] and [BMIM][NO3(-)] with HNO3 have been performed utilizing the polarizable, quantum chemistry based APPLE&P(®) potential. Experimentally it has been observed that [BMIM][DCA] exhibits hypergolic behavior when mixed with HNO3 while [BMIM][NO3(-)] does not. The structural, thermodynamic, and transport properties of the IL/HNO3 mixtures have been determined from equilibrium MD simulations over the entire composition range (pure IL to pure HNO3) based on bulk simulations. Additional (non-equilibrium) simulations of the composition profile for IL/HNO3 interfaces as a function of time have been utilized to estimate the composition dependent mutual diffusion coefficients for the mixtures. The latter have been employed in continuum-level simulations in order to examine the nature (composition and width) of the IL/HNO3 interfaces on the millisecond time scale.

Reactions of singly-reduced ethylene carbonate in lithium battery electrolytes: a molecular dynamics simulation study using the ReaxFF.

We have conducted quantum chemistry calculations and gas- and solution-phase reactive molecular dynamics simulation studies of reactions involving the ethylene carbonate (EC) radical anion EC(-) using the reactive force field ReaxFF. Our studies reveal that the substantial barrier for transition from the closed (cyclic) form, denoted c-EC(-), of the radical anion to the linear (open) form, denoted o-EC(-), results in a relatively long lifetime of the c-EC(-) allowing this compound to react with other singly reduced alkyl carbonates. Using ReaxFF, we systematically investigate the fate of both c-EC(-) and o-EC(-) in the gas phase and EC solution. In the gas phase and EC solutions with a relatively low concentration of Li(+)/x-EC(-) (where x = o or c), radical termination reactions between radical pairs to form either dilithium butylene dicarbonate (CH(2)CH(2)OCO(2)Li)(2) (by reacting two Li(+)/o-EC(-)) or ester-carbonate compound (by reacting Li(+)/o-EC(-) with Li(+)/c-EC(-)) are observed. At higher concentrations of Li(+)/x-EC(-) in solution, we observe the formation of diradicals which subsequently lead to formation of longer alkyl carbonates oligomers through reaction with other radicals or, in some cases, formation of (CH(2)OCO(2)Li)(2) through elimination of C(2)H(4). We conclude that the local ionic concentration is important in determining the fate of x-EC(-) and that the reaction of c-EC(-) with o-EC(-) may compete with the formation of various alkyl carbonates from o-EC(-)/o-EC(-) reactions.

Molecular dynamics simulation studies of the influence of imidazolium structure on the properties of imidazolium/azide ionic liquids.

Atomistic molecular dynamics simulations were performed on 1-butyl-3-methyl-imidazolium azide [bmim][N(3)], 1-butyl-2,3-dimethylimidazolium azide [bmmim][N(3)], and 1-butynyl-3-methyl-imidazolium azide [bumim][N(3)] ionic liquids. The many-body polarizable APPLE&P force field was augmented with parameters for the azide anion and the bumim cation. Good agreement between the experimentally determined and simulated crystal structure of [bumim][N(3)] as well as the liquid-state density and ionic conductivity of [bmmim][N(3)] were found. Methylation of bmim (yielding bmmim) resulted in dramatic changes in ion structuring in the liquid and slowing of ion motion. Conversely, replacing the butyl group of bmim with the smaller 2-butynyl group resulted in an increase of ion dynamics.

Density functional theory study of the role of anions on the oxidative decomposition reaction of propylene carbonate.

The oxidative decomposition mechanism of the lithium battery electrolyte solvent propylene carbonate (PC) with and without PF(6)(-) and ClO(4)(-) anions has been investigated using the density functional theory at the B3LYP/6-311++G(d) level. Calculations were performed in the gas phase (dielectric constant ε = 1) and employing the polarized continuum model with a dielectric constant ε = 20.5 to implicitly account for solvent effects. It has been found that the presence of PF(6)(-) and ClO(4)(-) anions significantly reduces PC oxidation stability, stabilizes the PC-anion oxidation decomposition products, and changes the order of the oxidation decomposition paths. The primary oxidative decomposition products of PC-PF(6)(-) and PC-ClO(4)(-) were CO(2) and acetone radical. Formation of HF and PF(5) was observed upon the initial step of PC-PF(6)(-) oxidation while HClO(4) formed during initial oxidation of PC-ClO(4)(-). The products from the less likely reaction paths included propanal, a polymer with fluorine and fluoro-alkanols for PC-PF(6)(-) decomposition, while acetic acid, carboxylic acid anhydrides, and Cl(-) were found among the decomposition products of PC-ClO(4)(-). The decomposition pathways with the lowest barrier for the oxidized PC-PF(6)(-) and PC-ClO(4)(-) complexes did not result in the incorporation of the fluorine from PF(6)(-) or ClO(4)(-) into the most probable reaction products despite anions and HF being involved in the decomposition mechanism; however, the pathway with the second lowest barrier for the PC-PF(6)(-) oxidative ring-opening resulted in a formation of fluoro-organic compounds, suggesting that these toxic compounds could form at elevated temperatures under oxidizing conditions.

Polypeptide grafted hyaluronan: A self-assembling comb-branched polymer constructed from biological components.

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(L-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(L-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.

An Analysis of Internet Searches Performed on a Hospital System Homepage to Assess Search Patterns and Traffic Generated by Radiology-specific Terms.

OBJECTIVE: To understand the utilization of the search engine within our hospital system's homepage, stratifying the searches into physician specialty, procedures or therapies, patient conditions, and logistical queries, with a specific focus on radiology-specific terms as a baseline to guide future interventions. METHODS: The top 1000 most searched terms entered into the medical system's homepage between January 1, 2017 and February 28, 2018 were collected. Related or similar terms were combined for analysis. RESULTS: During the study period, there were 121,071 unique searches on the center's website, and the top 1000 most searched terms combined for 65,011 searches. The most searched category was logistical queries (n = 29,667), followed by searches for conditions (n = 14,033), specialties (n = 3083), and procedures or therapies (n = 2252). Within the top 1000 most searched terms, radiology-specific searches accounted for 96 searches. These terms were all mammography-related. CONCLUSION: Radiology as a specialty and radiology-specific terms were not frequently searched for by patients when compared with other specialties. Mammography-related terms were the only radiologic subspecialty items within the top 1000 search terms. Overall, patients searched more for conditions than they did for specialties or therapies. These findings could be a representation of the general public's lack of awareness regarding the specialty.

Objective comparison of errors and report length between structured and freeform abdominopelvic computed tomography reports.

PURPOSE: To objectively compare structured and freeform abdominopelvic CT reports based on the number and types of errors as well as report length. METHODS: 90 structured and 89 freeform reports from abdominopelvic CT scans with IV contrast obtained for the indication of abdominal pain were randomly selected for review. Each report was reviewed for errors, which were counted and categorized based on the type of error. The total number of words in each report was tallied. RESULTS: 105 total errors were found in the structured reports, compared to 157 total errors in freeform reports. There were 1.16 errors per structured report and 1.76 errors per freeform report (p < 0.001). 48% of structured reports contained at least one error, while 71% of freeform reports contained at least one error (p = 0.002). When a difference existed between the styles with regard to error categories, more errors were observed in freeform reports, with the exception of the duplicated period error where structured reports had more errors. No difference on the basis of average words per report existed, with 219.2 words per report for each reporting style. CONCLUSION: The use of structured reporting for abdominopelvic CT results in less errors in the report when compared to freeform reporting, potentially reducing clinically significant adverse outcomes in patient care. The report length on the basis of number of words per report is not different between the two reporting styles.

Molecular insights into the potential and temperature dependences of the differential capacitance of a room-temperature ionic liquid at graphite electrodes.

Molecular dynamics simulation studies of the structure and the differential capacitance (DC) for the ionic liquid (IL) N-methyl-N-propylpyrrolidinium bis(trifluoromethane)sulfonyl imide ([pyr(13)][TFSI]) near a graphite electrode have been performed as a function temperature and electrode potential. The IL exhibits a multilayer structure that extends 20-30 Å from the electrode surface. The composition and ion orientation in the innermost layer were found to be strongly dependent on the electrode potential. While at potentials near the potential of zero charge (PZC), both cations and anions adjacent to the surface are oriented primarily perpendicular to the surface, the counterions in first layer orient increasingly parallel to the surface with increasing electrode potential. A minimum in DC observed around -1 V(RPZC) (potential relative to the PZC) corresponds to the point of highest density of perpendicularly aligned TFSI near the electrode. Maxima in the DC observed around +1.5 and -2.5 V(RPZC) are associated with the onset of "saturation", or crowding, of the interfacial layer. The asymmetry of DC versus electrode polarity is the result of strong interactions between the fluorine of TFSI and the surface, the relatively large footprint of TFSI compared to pyr(13), and the tendency of the propyl tails of pyr(13) to remain adsorbed on the surface even at high positive potentials. Finally, an observed decreased DC and the disappearance of the minimum in DC near the PZC with increasing temperature are likely due to the increasing importance of entropic/excluded volume effects (interfacial crowding) with increasing temperature.

Molecular dynamics simulations of atomically flat and nanoporous electrodes with a molten salt electrolyte.

The electric double layer (EDL) structure and capacitance have been studied for atomically flat and nanoporous conductive electrodes with a molten LiCl electrolyte using an electroactive interface molecular dynamics simulation methodology. For the atomically flat electrodes the electrolyte was observed to form a multilayer structure near the electrode described by exponentially decaying sinusoidal oscillations in ion and charge densities perpendicular to the electrode/electrolyte interface. The differential EDL capacitance vs. electrode potential was found to exhibit "U-shaped" behavior while the EDL capacitance exhibited complex dependence on electrode potential including regions of negative capacitance near zero electrode potential. Increased capacitance and an enhanced degree of electrode-electrolyte interface structure were observed with decreasing temperature. For nanoporous electrodes with both slit and cylindrical pore geometries, the electrolyte was observed to form highly structured alternating charged layers within the electrode nanopores. A maximum in the normalized (per unit electrode area) EDL capacitance was found for pore widths that accommodate several charged layers inside the pores. The observed dependence of capacitance on pore size appears to be a compromise between increasing structure/charge imbalance and decreasing ion density with decreasing pore width/diameter.

A comparison of fluoroalkyl-derivatized imidazolium:TFSI and alkyl-derivatized imidazolium:TFSI ionic liquids: a molecular dynamics simulation study.

Molecular dynamics simulations of fluoroalkyl-derivatized imidazolium:bis(trifluoromethylsulfonyl)imide (TFSI) room temperature ionic liquids (FADI-RTILs) with cations of the structure 1-F(CF(2))(n)(CH(2))(2)-3-methyl imidazolium have been performed and compared with simulations of alkyl-derivatized 1-H(CH(2))(n+2)-3-methyl imidazolium analogs (ADI-RTILs). Simulations yield RTIL densities, viscosities and ionic conductivities for the FADI-RTILs and ADI-RTILs in reasonably good agreement with experimental data. Partial fluorination results in a larger increase in density than would be anticipated based upon the density difference between perfluoralkane and alkane melts. Similarly, the slowing down in dynamics upon partial fluorination is greater than would be expected based upon the increase in cation volume. Examination of cation-cation, anion-anion and cation-anion centers-of-mass radial distribution functions reveal remarkably little influence of partial fluorination on the spherically averaged intermolecular structure of the RTILs. Similarly, simulations reveal little change in tail conformations and the extent of tail-tail aggregation upon partial fluorination. The interaction of the TFSI anion with the positively charged imidazolium ring hydrogen and nitrogen atoms is also little influenced by partial fluorination. However, the partially fluorinated alkyl tail exhibits increased interaction with the TFSI anion due to the electron withdrawing character of the fluorinated groups. We believe this strong tail-anion electrostatic interaction largely accounts for the higher than expected density and slower than expected dynamics in the FADI-RTILs.

Quantum chemistry and molecular dynamics simulation study of dimethyl carbonate: ethylene carbonate electrolytes doped with LiPF6.

Quantum chemistry studies of ethylene carbonate (EC) and dimethyl carbonate (DMC) complexes with Li+ and LiPF6 have been conducted. We found that Li+ complexation significantly stabilizes the highly polar cis-trans DMC conformation relative to the nearly nonpolar gas-phase low energy cis-cis conformer. As a consequence, the binding of Li+ to EC in the gas phase is not as favorable relative to binding to DMC as previously reported. Furthermore, quantum chemistry studies reveal that, when complexation of LiPF6 ion pairs is considered, the DMC/LiPF6 complex is about 1 kcal/mol more stable than the EC/LiPF6 complex. The EC3DMC(cis-cis)/Li+ complex was found to be the most energetically stable among ECnDMCm/Li+ (n+m=4) investigated complexes followed by EC4/Li+. Results of the quantum chemistry studies of these complexes were utilized in the development of a many-body polarizable force field for EC:DMC/LiPF6 electrolytes. Molecular dynamics (MD) simulations of EC/LiPF6, DMC/LiPF6, and mixed solvent EC:DMC/LiPF6 electrolytes utilizing this force field were performed at 1 M salt concentration for temperatures from 298 to 363 K. Good agreement was found between MD simulation predictions and experiments for thermodynamic and transport properties of both pure solvents and the electrolytes. We find increased ion pairing with increasing DMC content; however, both EC and DMC were found to participate in Li+ solvation in mixed EC:DMC electrolytes despite a huge difference in their dielectric constants. In contrast to previous NMR studies, where dominance of EC in cation solvation was reported, we find a slight preference for DMC in the cation solvation shell for EC:DMC (1 wt:1 wt) electrolytes and show that reanalyzed Raman spectroscopy experiments are in good agreement with results of MD simulations. Finally, analysis of solvent residence times reveals that cation transport is dominated by motion with solvating DMC and approximately equal contributions from vehicular motions with the first solvation shell and solvent exchange with respect to solvating EC.

Viscosity of a room temperature ionic liquid: predictions from nonequilibrium and equilibrium molecular dynamics simulations.

Nonequilibrium molecular dynamics (NEMD) simulations have been performed on 1-methyl-3-ethyl-imidazolium bis(trifluoromethane)sulfonimide [emim][Ntf(2)] using Lees-Edwards boundary conditions. A range of inverse shear rates corresponding to a fraction of the rotational relaxation time for the slowest relaxing molecular axis of anion and cation to 20 rotational relaxation times (1/20 tau(rot) < gamma < 5/tau(rot)) has been investigated. An extrapolation of the shear-rate-dependent viscosity obtained from these simulations to zero shear rate using the empirical three-parameter Carreau equation yielded excellent agreement with the viscosity obtained from equilibrium MD simulations. Based upon the Carreau equation fit to the simulation data, shear-thinning behavior was observed in [emim][Ntf(2)] for all shear rates investigated, implying that Newtonian behavior is observed in [emim][Ntf(2)] only for shear rates significantly lower than the inverse rotational relaxation time. A close resemblance between the apparent time-dependent viscosity extracted from equilibrium MD simulations and the shear-rate-dependent viscosity extracted from NEMD simulations has been found and discussed. MD simulations accurately predicted [emim][Ntf(2)] density, self-diffusion coefficients, heat of vaporization, and lattice parameters for the crystalline phase.

A molecular dynamics simulation study of LiFePO4/electrolyte interfaces: structure and Li+ transport in carbonate and ionic liquid electrolytes.

We have performed atomistic molecular dynamics (MD) simulations of the (010) surface of LiFePO(4) in contact with an organic liquid electrolyte (OLE), ethylene carbonate : dimethyl carbonate (3 : 7) with approximately 1 mol kg(-1) LiPF(6), and an ionic liquid-based electrolyte (ILE), 1-ethyl 3-methyl-imidazolium: bis(fluorosulfonyl)imide (EMIM(+) : FSI(-)) with approximately 1 mol kg(-1) LiFSI. Surface-induced structure that extends about 1 nm from the LiFePO(4) surface was observed in both electrolytes. The electrostatic potential at the LiFePO(4) surface was found to be negative relative to the bulk electrolyte reflecting an excess of negative charge from the electrolyte coordinating surface Li(+). In the ILE system negative surface charge is partially offset by a high density of EMIM(+) cations coordinating surface oxygen. The electrostatic potential exhibits a (positive) maximum about 3 A from the LiFePO(4) surface which, when combined with the reduced ability of the highly structured electrolytes to solvate Li(+) cations, results in a free energy barrier of almost 4 kcal mol(-1) for penetration of the interfacial electrolyte layer by Li(+). The resistance for bringing Li(+) from the bulk electrolyte to the LiFePO(4) surface through this interfacial barrier was found to be small for both the OLE and ILE. However, we find that the ability of EMIM(+) cations to donate positive charge to LiFePO(4)/electrolyte interface may result in a significant decrease in the concentration of Li(+) at the surface and a corresponding increase in impedance to Li(+) intercalation into LiFePO(4), particularly at lower temperatures.

Shock-induced transformations in crystalline RDX: a uniaxial constant-stress Hugoniostat molecular dynamics simulation study.

Molecular dynamics (MD) simulations of uniaxial shock compression along the [100] and [001] directions in the alpha polymorph of hexahydro-1,3,5-trinitro-1,3,5-triazine (alpha-RDX) have been conducted over a wide range of shock pressures using the uniaxial constant stress Hugoniostat method [Ravelo et al., Phys. Rev. B 70, 014103 (2004)]. We demonstrate that the Hugoniostat method is suitable for studying shock compression in atomic-scale models of energetic materials without the necessity to consider the extremely large simulation cells required for an explicit shock wave simulation. Specifically, direct comparison of results obtained using the Hugoniostat approach to those reported by Thompson and co-workers [Phys. Rev. B 78, 014107 (2008)] based on large-scale MD simulations of shocks using the shock front absorbing boundary condition (SFABC) approach indicates that Hugoniostat simulations of systems containing several thousand molecules reproduced the salient features observed in the SFABC simulations involving roughly a quarter-million molecules, namely, nucleation and growth of nanoscale shear bands for shocks propagating along the [100] direction and the polymorphic alpha-gamma phase transition for shocks directed along the [001] direction. The Hugoniostat simulations yielded predictions of the Hugoniot elastic limit for the [100] shock direction consistent with SFABC simulation results.

A molecular dynamics simulation study of crystalline 1,3,5-triamino-2,4,6-trinitrobenzene as a function of pressure and temperature.

Quantum chemistry-based dipole polarizable and nonpolarizable force fields have been developed for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Molecular dynamics simulations of TATB crystals were performed for hydrostatic pressures up to 10 GPa at 300 K and for temperatures between 200 and 400 K at atmospheric pressure. The predicted heat of sublimation and room-temperature volumetric hydrostatic compression curve were found to be in good agreement with available experimental data. The hydrostatic compression curves for individual unit cell parameters were found to be in reasonable agreement with those data. The pressure- and temperature-dependent second-order isothermal elastic tensor was determined for temperatures between 200 and 400 K at normal pressure and for pressures up to 10 GPa on the 300 K isotherm. Simulations indicate considerable anisotropy in the mechanical response, with modest softening and significant stiffening of the crystal with increased temperature and pressure, respectively. For most properties the polarizable potential was found to yield better agreement with available experimental properties.

A molecular dynamics simulation study of the pressure-volume-temperature behavior of polymers under high pressure.

Isothermal compression of poly (dimethylsiloxane), 1,4-poly(butadiene), and a model Estane (in both pure form and a nitroplasticized composition similar to PBX-9501 binder) at pressures up to 100 kbars has been studied using atomistic molecular dynamics (MD) simulations. Comparison of predicted compression, bulk modulus, and U(s)-u(p) behavior with experimental static and dynamic compression data available in the literature reveals good agreement between experiment and simulation, indicating that MD simulations utilizing simple quantum-chemistry-based potentials can be used to accurately predict the behavior of polymers at relatively high pressure. Despite their very different zero-pressure bulk moduli, the compression, modulus, and U(s)-u(p) behavior (including low-pressure curvature) for the three polymers could be reasonably described by the Tait equation of state (EOS) utilizing the universal C parameter. The Tait EOS was found to provide an excellent description of simulation PVT data when the C parameter was optimized for each polymer. The Tait EOS parameters, namely, the zero-pressure bulk modulus and the C parameter, were found to correlate well with free volume for these polymers as measured in simulations by a simple probe insertion algorithm. Of the polymers studied, PDMS was found to have the most free volume at low pressure, consistent with its lower ambient pressure bulk modulus and greater increase in modulus with increasing pressure (i.e., crush-up behavior).

Molecular dynamics simulation study of spherical nanoparticles in a nematogenic matrix: anchoring, interactions, and phase behavior.

Molecular dynamics simulations of spherical nanoparticles (NPs) in a nematogenic matrix of soft spherocylinders (SSCs) with equal NP diameter and SSC length were performed. The NPs were found to be dispersed in the isotropic SSC matrix. At higher pressure, the NP-SSC mixture demixed into a NP-poor nematic phase and a NP-rich isotropic phase over most of the composition range investigated. However, at low NP concentrations a single-phase nematic with dispersed NPs was observed, while at very high NP concentration no nematic phase was observed. When the NP-SSC interactions were changed to promote homeotropic anchoring, the matrix-induced interaction between NPs in the isotropic SSC matrix exhibited strong intermediate-range repulsion that was expected to result in even greater dispersion of NPs. However, many-body effects appear to dominate NP-NP interactions in the isotropic SSC matrix with homeotropic anchoring even at the lowest NP concentration investigated, resulting in suppression of the intermediate range repulsion leading to aggregation of the NPs.

Passive transport of C60 fullerenes through a lipid membrane: a molecular dynamics simulation study.

To investigate the implications of the unique properties of fullerenes on their interaction with and passive transport into lipid membranes, atomistic molecular dynamics simulations of a C60 fullerene in a fully hydrated di-myristoyl-phoshatidylcholine lipid membrane have been carried out. In these simulations the free energy and the diffusivity of the fullerene were obtained as a function of its position within the membrane. These properties were utilized to calculate the permeability of fullerenes through the lipid membrane. Simulations reveal that the free energy decreases as the fullerene passes from the aqueous phase, through the head group layer and into the hydrophobic core of the membrane. This decrease in free energy is not due to hydrophobic interactions but rather to stronger van der Waals (dispersion) interactions between the fullerene and the membrane compared to those between the fullerene and (bulk) water. It was found that there is no free energy barrier for transport of a fullerene from the aqueous phase into the lipid core of the membrane. In combination with strong partitioning of the fullerenes into the lipidic core of the membrane, this "barrierless" penetration results in an astonishingly large permeability of fullerenes through the lipid membrane, greater than observed for any other known penetrant. When the strength of the dispersion interactions between the fullerene and its surroundings is reduced in the simulations, thereby emulating a nanometer sized hydrophobic particle, a large free energy barrier for penetration of the head group layer emerges, indicating that the large permeability of fullerenes through lipid membranes is a result of their unique interaction with their surrounding medium.