The Journal of Chemical Physics
Editors' Choice for 2010

Communication: Ab initio dynamics of rare thermally activated reactions
S. a Beccara, G. Garberoglio, P. Faccioli, and F. Pederiva

This method is based on the path integral representation for the stochastic dynamics and yields the time evolution of both nuclear and electronic degrees of freedom, along the most probable reaction pathways, without spending computational time to explore metastable states. As a first illustrative application, the authors characterize the dominant pathway in the cyclobutene → butadiene reaction, using the semiempirical Parametrized Model 3 approach.

J. Chem. Phys. 132, 111102 (2010)

Communication: The electronic spectrum of Li(NH₃)₄
Luigi Varriale, Nicola M. Tonge, Nitika Bhalla, and Andrew M. Ellis

This paper reports on the first electronic spectrum of Li(NH₃)₄ in the gas phase, which was recorded using mass-selective depletion spectroscopy. The broad and structured spectrum confirms a recent theoretical prediction that the electronic spectrum of Li(NH₃)₄ will strongly overlap with the spectrum of the solvated electron in lithium-ammonia solutions.

J. Chem. Phys. 132, 161101 (2010)

Communication: Exceptions to the d-band model of chemisorption on metal surfaces: The dominant role of repulsion between adsorbate states and metal d-states
H. Xin and S. Linic

Shown here is a family of adsorbate-substrate systems that do not follow the trends in adsorption energies predicted by the d-band model. A physically transparent model is used to analyze this phenomenon. It was found that these adsorbate-substrate pairs are characterized by the repulsive interaction of the substrate d-band with the renormalized adsorbate states.

J. Chem. Phys. 132, 221101(2010)

Communication: Accurate and efficient approximations to explicitly correlated coupled-cluster singles and doubles, CCSD-F12
Christof Hättig, David P. Tew, and Andreas Köhn

The explicitly correlated coupled-cluster singles and doubles CCSD-F12 method returns near basis set limit CCSD energies using only double- or triple-ζ orbital basis sets. However, the additional computational cost of the F12 contributions to the amplitude equations is considerable, which renders this method impractical for general applications. In this article, a new model CCSD(F12) is communicated, which has a computational cost close to that of conventional CCSD, while retaining the accuracy of CCSD(F12).

J. Chem. Phys. 132, 231102 (2010)

Communication: The ionization and dissociation energies of HD
Daniel Sprecher, Jinjun Liu, Christian Jungen, Wim Ubachs, and Frédéric Merkt

The adiabatic ionization energy and the dissociation energy of HD have been determined using a hybrid experimental-theoretical method. Combining measurements with highly accurate theoretical values of the ionization energies of the one-electron systems H, D, and HD⁺ further enabled a new determination of the dissociation energy of HD.

J. Chem. Phys. 133, 111102 (2010)

Communication: Heavy Rydberg states: The H⁺H⁻ system
Adam Kirrander

Heavy Rydberg states are analogs of electronic Rydberg states, but with the electron replaced by a much heavier ion. The authors calculate ab initio the extremely long-range vibrational H⁺H⁻ heavy Rydberg states in H₂, and compare these to recent experiments. The calculated resonance positions and widths agree well with experiment, but the authors predict additional sharp interloper resonances corresponding to vibrational states trapped inside the barrier on potential energy curve 7 ¹Σ_g⁺.

J. Chem. Phys. 133, 121103 (2010)

Ring polymer molecular dynamics beyond the linear response regime: Excess electron injection and trapping in liquids
Artur R. Menzeleev and Thomas F. Miller

Ring polymer molecular dynamics is used to simulate the dynamics of excess electron injection into fluid helium and liquid water. A method for modulating the initial energy of the excess electron is presented, and used to study both low-energy (cold) and high-energy (hot) electron injections.

J. Chem. Phys. 132, 034106 (2010)

A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu
Stefan Grimme, Jens Antony, Stephan Ehrlich, and Helge Krieg

This work refines the method of dispersion correction as an add-on to standard Kohn–Sham density functional theory (DFT-D), regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers.

J. Chem. Phys. 132, 154104 (2010)

High-order expansion of T₂×t₂ Jahn–Teller potential-energy surfaces in tetrahedral molecules
Daniel Opalka and Wolfgang Domcke

Methods from Jahn–Teller theory and invariant theory have been combined for the construction of analytic diabatic potential-energy surfaces of triply degenerate states in tetrahedral molecules. The potentials of a threefold degenerate electronic state of T₂ symmetry, subject to the T₂×t₂ or T₂×(t₂+t₂) Jahn–Teller effect in a three-dimensional or six-dimensional space of nuclear coordinates, respectively, are considered.

J. Chem. Phys. 132, 154108 (2010)

Effects of patch size and number within a simple model of patchy colloids
Achille Giacometti, Fred Lado, Julio Largo, Giorgio Pastore, and Francesco Sciortino

Computer simulation and integral equation methods are applied to patchy colloids, modeled as spheres whose surfaces are decorated with two opposite attractive caps. It is found that the gas-liquid critical point moves to lower densities and temperatures with decreasing patch size. A rich variety of structures in crystal and fluid phases are found as the coverage is varied.

J. Chem. Phys. 132, 174110 (2010)

A homogeneous nonequilibrium molecular dynamics method for calculating the heat transport coefficient of mixtures and alloys
K. K. Mandadapu, R. E. Jones, and P. Papadopoulos

This work generalizes Evans’ homogeneous nonequilibrium method for estimating heat transport coefficient to multispecies molecular systems described by general multibody potentials. The proposed method, in addition to being compatible with periodic boundary conditions, is shown to satisfy all the requirements of Evans’ original method, namely, adiabatic incompressibility of phase space, equivalence of the dissipative and heat fluxes, and momentum preservation.

J. Chem. Phys. 133, 034122 (2010)

Rung 3.5 density functionals
Benjamin G. Janesko

This work proposes a new term on the “Jacob’s ladder” of approximate exchange-correlation functionals in Kohn–Sham density functional theory. In these Rung 3.5 functionals, intermediate in complexity between the semilocal approximations of Rungs 1–3 and fully nonlocal Rung 4 approximations, the exchange-correlation energy density at a point depends linearly (rather than quadratically) on the nonlocal Kohn–Sham one-particle density matrix in a finite neighborhood around the point.

J. Chem. Phys. 133, 104103 (2010)

Imaging mesoscopic nuclear spin noise with a diamond magnetometer
Carlos A. Meriles, Liang Jiang, Garry Goldstein, Jonathan S. Hodges, Jeronimo Maze, Mikhail D. Lukin, and Paola Cappellaro

A novel NMR probe is described using a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. Such a sensor is able to probe the fluctuations of the “classical” dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample.

J. Chem. Phys. 133, 124105 (2010)

Density cumulant functional theory: First implementation and benchmark results for the DCFT-06 model
Andrew C. Simmonett, Jeremiah J. Wilke, Henry F. Schaefer, III, and Werner Kutzelnigg

This work implements density cumulant functional theory for the first time. Benchmark results are provided for atoms and diatomic molecules, demonstrating the performance of DCFT-06 for both nonbonded and bonded interactions.

J. Chem. Phys. 133, 174122 (2010)

Application of second-order Møller–Plesset perturbation theory with resolution-of-identity approximation to periodic systems
Michio Katouda and Shigeru Nagase

Electron correlation plays an important role in the accurate description of the conductive, optical, and magnetic properties of periodic systems. An efficient periodic boundary condition resolution-of-identity MP2 method is developed here, based on the crystal orbital formalism and applicable to the calculations of large periodic systems. In this method, the slow convergence problem of lattice sum of long-range atomic orbital electron repulsion integrals in Fourier transformations was avoided by the use of Poisson and Gaussian mixed auxiliary basis functions.

J. Chem. Phys. 133, 184103 (2010)

Quantum theory of molecular collisions in a magnetic field: Efficient calculations based on the total angular momentum representation
T. V. Tscherbul and A. Dalgarno

An efficient method is presented for rigorous quantum calculations of atom-molecule and molecule-molecule collisions in a magnetic field. The method is based on the expansion of the wave function of the collision complex in basis functions with well-defined total angular momentum in the body-fixed coordinate frame.

J. Chem. Phys. 133, 184104 (2010)

Nonlocal van der Waals density functional: The simpler the better
Oleg A. Vydrov and Troy Van Voorhis

The authors here devise a nonlocal correlation energy functional that describes the entire range of dispersion interactions in a seamless fashion using only the electron density as input. The new functional is considerably simpler than its predecessors of a similar type. The functional has a tractable and robust analytic form that lends itself to efficient self-consistent implementation. The functional proposed in this work is a computationally inexpensive electronic structure tool of broad applicability.

J. Chem. Phys. 133, 244103 (2010)

Time-resolved photoelectron imaging of ultrafast S₂→S₁ internal conversion through conical intersection in pyrazine
Yoshi-Ichi Suzuki, Takao Fuji, Takuya Horio, and Toshinori Suzuki

A nonadiabatic electronic transition through a conical intersection was studied by pump-probe photoelectron imaging spectroscopy with a 22 fs time resolution in the benchmark polyatomic molecule of pyrazine and deuterated pyrazine.

J. Chem. Phys. 132, 174302 (2010)

Photofragment angular momentum distributions in the molecular frame. II. Single state dissociation, multiple state interference, and nonaxial recoil in photodissociation of polyatomic molecules
T. Peter Rakitzis and Andrew J. Alexander

In this paper an a_q^k(s) polarization-parameter model is presented to describe product angular momentum polarization from the one-photon photodissociation of polyatomic molecules in the molecular frame. This model is applied to the linearly polarized photodissociation of polyatomic molecules and to dissociation mechanisms with nonaxial recoil and multiple state interference, giving insight into geometrical properties.

J. Chem. Phys. 132, 224310 (2010)

Valence photoelectron spectroscopy of N₂ and CO: Recoil-induced rotational excitation, relative intensities, and atomic orbital composition of molecular orbitals
T. D. Thomas, E. Kukk, T. Ouchi, A. Yamada, H. Fukuzawa, K. Ueda, R. Püttner, I. Higuchi, Y. Tamenori, T. Asahina, N. Kuze, H. Kato, M. Hoshino, H. Tanaka, A. Lindblad, and L. J. Sæthre

Recoil-induced rotational excitation accompanying photoionization has been measured for the X, A, and B states of N₂⁺ and CO⁺ over a range of photon energies from 60 to 900 eV. These measurements provide a tool for investigating the atomic orbital composition of the molecular orbitals.

J. Chem. Phys. 133, 174312 (2010)

Dipole moment surface of the van der Waals complex CH₄–N₂
N. Zvereva-Loëte, Y. N. Kalugina, V. Boudon, M. A. Buldakov, and V. N. Cherepanov

The interaction-induced dipole moment surface of the van der Waals CH₄–N₂ complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules at the MP2 and CCSD(T) levels of theory using the correlation-consistent aug-cc-pVTZ basis set with the basis set superposition error correction.

J. Chem. Phys. 133, 184302 (2010)

Water binding sites in 2-para- and 2-ortho-fluorophenylethanol: A high-resolution UV experiment and ab initio calculations
R. Karaminkov, S. Chervenkov, and H. J. Neusser

The singly hydrated complexes of the flexible prototype molecules 2-para- and 2-ortho-fluorophenylethanol have been investigated by combination of high-resolution resonance-enhanced two-photon ionization spectroscopy in a cold supersonic beam and quantum chemistry ab initio calculations. Conformational structures of the above complexes are identified, which correspond to water binding to the most stable gauche monomer’s conformers in both cases.

J. Chem. Phys. 133, 194301 (2010)

Rotational dependence of the proton-transfer reaction HBr⁺ + CO₂ → HOCO⁺ + Br. II. Comparison of HBr⁺ (²Π_3/2) and HBr⁺ (²Π_1/2)
Lisa Paetow, Franziska Unger, Bernd Beutel, and Karl-Michael Weitzel

The effects of reactant ion rotational excitation on the exothermic proton-transfer reactions of HBr⁺ (²Π_3/2) and DBr⁺ (²Π_3/2), respectively, with CO₂ were studied in a guided ion beam apparatus. The reaction cross section decreases with increasing rotational energy, however, the dependence changes with collision energy.

J. Chem. Phys. 133, 234301 (2010)

Recombination-pumped triatomic hydrogen infrared lasers
R. J. Saykally, E. A. Michael, J. Wang, and Chris H. Greene

Mid-infrared laser lines observed in hydrogen/rare gas discharges are assigned to three-body recombination processes involving an electron, a rare gas (He or Ne) atom, and the triatomic hydrogen ion (H₃⁺). Calculations of radiative transitions between neutral H₃ Rydberg states support this interpretation, and link it to recent results for hydrogenic/rare gas afterglow plasmas.

J. Chem. Phys. 133, 234302 (2010)

Proton disorder and the dielectric constant of type II clathrate hydrates
Steven W. Rick and David L. Freeman

Computational studies are presented examining the degree of proton disorder, the dielectric properties, and the molar volumes of sII clathrate hydrates with argon and H₂ in aqueous cages. The extent of proton disorder is found to be insensitive to the guest identity. The dielectric constants of clathrates are found to be smaller than that of ice, mainly due to the lower densities of the clathrate systems.

J. Chem. Phys. 132, 054509 (2010)

Calculations of vibrationally resonant sum- and difference-frequency-generation spectra of chiral molecules in solutions: Three-wave-mixing vibrational optical activity
Jun-Ho Choi, Sangheon Cheon, and Minhaeng Cho

Quantum chemistry calculations were carried out to obtain nonlinear optical properties for a  representative chiral molecule, (S)-methyl lactate, and numerically simulate the corresponding spectra. It is shown that the circular polarization three-wave-mixing signal intensities are quantitatively similar to those of the linear polarization three-wave-mixing signals, and that they are sensitive to the absolute configuration of the chiral molecule.

J. Chem. Phys. 132, 074506 (2010)

An exciton scattering model for carrier multiplication in semiconductor nanocrystals: Theory
Andrei Piryatinski and Kirill A. Velizhanin

The effect of carrier multiplication  in semiconductor nanocrystals is systematically treated by employing an exciton scattering approach. Using projection operators, the Coulomb coupled multiexciton dynamics is reduced to scattering dynamics in the space spanning both single- and biexciton states.

J. Chem. Phys. 133, 084508 (2010)

Product gas evolution above planar microstructured model catalysts—A combined scanning mass spectrometry, Monte Carlo, and computational fluid dynamics study
M. Roos, J. Bansmann, D. Zhang, O. Deutschmann, and R. J. Behm

The transport and distribution of reaction products above catalytically active Pt micro-structures was studied by spatially resolved scanning mass spectrometry  in combination with Monte Carlo simulation and fluid dynamics calculations, using the oxidation of CO as test reaction.   Measurement and reaction conditions are defined where effects induced by the capillary tip can be neglected (‘minimal invasive measurements’) and provide a basis for the evaluation of catalyst activities on microstructured model systems.

J. Chem. Phys. 133, 094504 (2010)

Preferential solvation dynamics in liquids: How geodesic pathways through the potential energy landscape reveal mechanistic details about solute relaxation in liquids
Crystal N. Nguyen and Richard M. Stratt

The dynamics of preferential solvation is studied for geodesic paths in a simple atomic liquid mixture. The mechanism for preferential solvation features a reasonably sharp onset for slow diffusion, and this diffusion involves a sequential, rather than concerted, series of solvent exchanges.

J. Chem. Phys. 133, 124503 (2010)

Watching solvent friction impede ultrafast barrier crossings: A direct test of Kramers theory
Jessica M. Anna and Kevin J. Kubarych

Two-dimensional infrared chemical exchange spectroscopy is used to systematically investigate how solvent dynamics influence activated barrier crossings on an electronic ground state. Use of the electronic ground state facilitates a direct comparison with Kramers theory of condensed phase reaction kinetics and avoids the significant complication of electronic excitation. For the first time, an electronic ground state with a well-defined transition state is directly probed in the time domain.

J. Chem. Phys. 133, 174506 (2010)

Fokker–Planck analysis of separation dependent potentials and diffusion coefficients in simulated microscopy experiments
Daniel J. Beltran-Villegas, Ray M. Sehgal, Dimitrios Maroudas, David M. Ford, and Michael A. Bevan

The authors developed a Fokker–Planck formalism to simultaneously extract both particle-surface interaction potentials and position-dependent diffusion coefficients. Their results demonstrate the ability to extract both static and dynamic information from microscopy measurements of isolated particles near surfaces, which provides a foundation for further investigation of particle ensembles and nonequilibrium systems.

J. Chem. Phys. 132, 044707 (2010)

Structure and infrared absorption of the first layer C₂H₂ on the NaCl(100) single-crystal surface
A. G. Cabello-Cartagena, J. Vogt, and H. Weiss

The adsorbate structure of the first layer acetylene on the NaCl(100) single-crystal surface is investigated using polarization infrared spectroscopy in combination with low-energy electron diffraction (LEED) experiments, and potential calculations on the basis of pair potentials. Total energy minimizations support a new structure model which contains five inequivalent molecules per unit cell in a herringbone arrangement. The application of a vibrational exciton approach demonstrates that this new structure model can reproduce the triplet spectrum observed in the infrared experiments.

J. Chem. Phys. 132, 074706 (2010)

Direct and indirect electron transfer at a semiconductor surface with an adsorbate: Theory and application to Ag₃Si(111):H
Andrew S. Leathers, David A. Micha, and Dmitri S. Kilin

A theoretical and computational study of photoinduced electron transfer between a metal cluster and a semiconductor surface is presented. Results obtained using electronic parameters from ab initio density functional calculations for the Ag₃Si(111):H system photoexcited by visible light show that indirect electron transfer is much more likely than direct transfer and to lead to longer lasting electronic charge separation.

J. Chem. Phys. 132, 114702 (2010)

Observation of low heat capacities for vapor-deposited glasses of indomethacin as determined by AC nanocalorimetry
Kenneth L. Kearns, Katherine R. Whitaker, M. D. Ediger, Heiko Huth, and Christoph Schick

Alternating current nanocalorimetry was used to evaluate the heat capacity and kinetic stability of highly stable glass films of indomethacin (IMC) prepared by physical vapor deposition as a function of thickness. Interpretation of results indicate that the transformation of stable glass into supercooled liquid can occur by either a surface-initiated or bulk mechanism. In these experiments, the structural relaxation time of the IMC supercooled liquid was observed to be nearly independent of sample thickness.

J. Chem. Phys. 133, 014702 (2010)

Electronic effects of single H atoms on Ge(001) revisited
G. A. Shah, M. W. Radny, P. V. Smith, S. R. Schofield, and N. J. Curson

The adsorption of isolated H atoms on the Ge(001) surface is studied using density functional theory (DFT) and scanning tunnelling microscopy. Two stable adsorption positions that are found in DFT correspond to H atom attachment to an up- or down-buckled Ge dimer atom, respectively. Surprisingly, in the case where H bonds to the down-buckled Ge atom, it was found that there is a redistribution of a unit of charge which leaves the net charge of the doubly occupied dangling bond of the unreacted Ge atom intact.

J. Chem. Phys. 133, 014703 (2010)

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH₃–Si(111) and CD₃–Si(111) surfaces
James S. Becker, Ryan D. Brown, Erik Johansson, Nathan S. Lewis, and S. J. Sibener

The surface structure and vibrational dynamics of CH₃–Si(111) and CD₃–Si(111) surfaces were measured using helium atom scattering. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. Experiments presented yield detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces.

J. Chem. Phys. 133, 104705 (2010)

DFT+U study of defects in bulk rutile TiO₂
Jess Stausholm-Møller, Henrik H. Kristoffersen, Berit Hinnemann, Georg K. H. Madsen, and Bjørk Hammer

Rutile titanium dioxide (titania) is the most studied transition metal oxide within surface science. Electronic gap states in defected titania are studied using the Hubbard-U approximation in the grid-based projector-augmented wave density functional theory code. The defects considered are titanium interstitials, oxygen vacancies, and hydrogen dopants in the rutile phase of bulk titanium dioxide.

J. Chem. Phys. 133, 144708 (2010)

A numerical study of mobility in thin films of fullerene derivatives
Roderick C. I. MacKenzie, Jarvist M. Frost, and Jenny Nelson

Electron mobility in films of fullerene derivatives is investigated numerically by attaching aliphatic chains to the C₆₀ cage. Molecular dynamics is used to generate film morphology, quantum chemical methods to calculate intermolecular charge transfer rates, and Monte Carlo methods to simulate time-of-flight experiments. It is found that as the length of the aliphatic side chain increases, the configurational disorder increases and thus the mobility decreases.

J. Chem. Phys. 132, 064904 (2010)

General approach to polymer chains confined by interacting boundaries
Karl F. Freed, Jacek Dudowicz, Evgeny B. Stukalin, and Jack F. Douglas

This article takes a general approach to describing polymers under conditions of weak to moderate confinement and applies this semianalytic method specifically to determine the thermodynamics and static structure factor for a flexible polymer confined between impenetrable interacting parallel plate boundaries.

J. Chem. Phys. 132, 094901 (2010)

Coupling of twist and writhe in short DNA loops
Shlomi Medalion, Shay M. Rappaport, and Yitzhak Rabin

In order to study the coupling between the writhe and twist distributions for various DNA lengths, Monte Carlo simulations were performed for wormlike rods. For sufficiently short DNA, the writhe distribution differs from that of a model with bending energy only. The simulation results are compared with a factorization approximation and experimental tests are proposed.

J. Chem. Phys. 132, 045101 (2010)

Nucleation theory with delayed interactions: An application to the early stages of the receptor-mediated adhesion/fusion kinetics of lipid vesicles
Antonio Raudino and Martina Pannuzzo

This research reports on the development of semiquantitative theory aimed at describing the adhesion kinetics between soft objects, such as living cells or vesicles. In addition, the investigators  look at the effect of the ligand-receptor pairing kinetics at the adhesion site in the time course of the patch expansion.

J. Chem. Phys. 132, 045103 (2010)

Effects of side-chain packing on the formation of secondary structures in protein folding
Satoshi Yasuda, Takashi Yoshidome, Hiraku Oshima, Ryota Kodama, Yuichi Harano, and Masahiro Kinoshita

The entropy of water plays an important role in protein folding. This paper investigates the specific role that side-chain packing plays in increasing water entropy for α-helix and β-sheet secondary structures.

J. Chem. Phys. 132, 065105 (2010)

Probing single nanometer-scale pores with polymeric molecular rulers
Sarah E. Henrickson, Edmund A. DiMarzio, Qian Wang, Vincent M. Stanford, and John J. Kasianowicz

This paper shows that polynucleotides can be used to probe structural features of the α-hemolysin channel.   Specifically, both the pore length and channel aperture profile can be estimated. The results are consistent with the channel crystal structure and suggest that polymer-based “molecular rulers” may prove useful in deducing the structures of nanometer-scale pores in general.

J. Chem. Phys. 132, 135101 (2010)

DNA-protein binding rates: Bending fluctuation and hydrodynamic coupling effects
Yann von Hansen, Roland R. Netz, and Michael Hinczewski

Diffusion-limited reactions between a diffusing particle and a target site on a semiflexible polymer, a key factor determining the kinetics of DNA-protein binding and polymerization of cytoskeletal filaments, are investigated. The theory presented focuses on two competing effects: polymer shape fluctuations, which speed up association, and the hydrodynamic coupling between the diffusing particle and the chain, which slows down association.

J. Chem. Phys. 132, 135103 (2010)

The electrostatics of solvent and membrane interfaces and the role of electronic polarizability
Igor Vorobyov and Toby W. Allen

The electrostatics of solvent and lipid bilayer interfaces are investigated with the aim of understanding the interaction of ions and charged peptides with biological membranes.

J. Chem. Phys. 132, 185101 (2010)

Slow molecular dynamics close to crystal surfaces during crystallization of a protein lysozyme studied by fluorescence correlation spectroscopy
S. Tanaka

Fluorescence correlation spectroscopy was applied to the crystallization processes of egg-white lysozyme to investigate the molecular dynamics less than one micron from crystal surfaces of both tetragonal single crystals and needlelike spherulites. The  observations are explained as arising from aggregates of needlelike crystals that mature to form single crystals.

J. Chem. Phys. 133, 095103 (2010)

Atomistic theory of amyloid fibril nucleation
Raffaela Cabriolu, Dimo Kashchiev, and Stefan Auer

This work considers the nucleation of amyloid fibrils at the molecular level when the process takes place by a direct polymerization of peptides or protein segments into β-sheets. The analysis illustrates a  unique feature of atomistic nucleation theory  that the size of the fibril nucleus is a constant integer in a given supersaturation range. The results obtained are applicable to homogeneous nucleation, which occurs when the protein solution is sufficiently pure and/or strongly supersaturated.

J. Chem. Phys. 133, 225101 (2010)