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Water oxidation of photosynthesis at the oxygen evolving complex (OEC) is driven by the polarization field induced by the photoelectric hole. By highlighting the role of the polarization field in reshaping the spin and orbit potentials, we reveal in this work the characteristics and underlying mechanism in the relatively simpler OEC evolutions within the states S0 - S2 prior to the water oxidation. The characteristic shifts of the density of states (DOS) of the electron donor Mn atom are observed in the vicinity of the Fermi surface to occur with the spin flips of Mn atoms and the change of the Mn oxidation states during the electron transfer. Notably, the spin flips of Mn atoms point to the resulting spin configuration of the next states. It is found that the electron transfer tend to stabilize the catalyst OEC itself, whereas the proton transfer pushes the evolution forward by preparing a new electron donor, demonstrating the proton-coupled electron transfer. Meanwhile, it shows that the Mn-O bonds around the candidate Mn atom of the electron donor undergo characteristic changes in the bond lengths during the electron transfer. These concomitant phenomena uncovered in first-principle calculations characterize the essential equilibrium of the OEC between the state evolution and stability that forms a ground of the dynamic OEC cycles. In particular, the characteristic undulation of the DOS around the Fermi level occurring at the proton-coupled electron transfer can be used to reveal crucial processes in a wide range of realistic systems.

Water oxidation at the oxygen evolving complex (OEC) of the photosystem II is catalyzed by the core cluster CaMn$_4$O$_5$ which was projected to experience five intermediate states S$\rm_i$ in the Kok's cycle since 1970's. However, the detailed dynamics of state evolutions still remains unclear, albeit with the general fact that the process is initiated by the transfer of photoelectrons with the steady electron donors of the water molecules. Based on density functional simulations, we find that the spin flips of Manganese atoms between the consecutive states in the electric polarization field can be used as a marker to uncover the intricate dynamic evolutions and the underlying dynamics. The dynamic electron and proton transfers and water insertion and dissociation are traced to reveal the evolution pathways of S$_0$-S$_3$ with commensurate spin flips towards the exact spin configuration of the next state. In particular, the various water insertions and dissociations at coordination sites of the S$_2$ open and closed cubane isomers are predicted with constraints on the necessary spin flips. Our study paves a way to uncover the animated OEC evolutions with the spin flips that await for more experimental verifications and lays a solid ground for revealing the mechanism of dioxygen generation via the pending S$_4$ state., Comment: 8 pages, 5 figures

We study the neutron star core-crust transition density $\rho_t$ with the inclusion of the vacuum polarization in the dielectric function in the nonlinear relativistic Hartree approach (RHAn). It is found that the strong correlation between the $\rho_{t}$ and the scalar meson mass $m_{\sigma}$ strikingly overwhelms the uncertainty of the nuclear equation of state in the RHAn models, in contrast to the usual awareness that $\rho_{t}$ is predominantly sensitive to the isovector nuclear potential and symmetry energy. The accurate extraction of $\rho_{t}$ through the future gravitational wave measurements can thus provide a strong constraint on the longstanding uncertainty of $m_{\sigma}$, which is of significance to better infer the vacuum property. As an astrophysical implication, it suggests that the correlation between $\rho_t$ and $m_\sigma$ is very favorable to reconcile the difficulty in reproducing the large crustal moment of inertia for the pulsar glitches with the well constrained symmetry energy., Comment: 11 pages, 4 figures

The mid-infrared heating of interfacial water with different initial temperatures is studied using non-equilibrium molecular dynamics simulation. It is found that under the irradiation of a pulse at 3360-3380 $cm^{-1}$ the two-dimensional water monolayer on a hydrophilic surface at a lower initial temperature acquires a much larger temperature jump. The mechanism beneath this counterintuitive phenomenon is the enhanced transition efficiency of the asymmetric OH stretching vibration due to the specific oriented configuration of water molecules at lower initial temperatures. The understanding of the anomalous phenomenon clarifies the sensitivity of the interfacial properties of water molecules to the temperature.

The energy absorption on nanometer scale is vital for many bio and chemical systems. We report here that a two times amplification in absorption efficiency can be achieved by water molecules confined in carbon nanotubes with small radius, compared with situations in normal bulk water, under irradiations of short mid-infrared pulses. The effect of confinement due to a (6,6) carbon nanotube is found to be very robust, equivalent to that of a 5 $V/nm$ static electric field. These findings are instructive not only for designing high-efficiency nano devices but also for understanding behaviours in biological channels.

The energy acquisition based on resonant excitations are of great importance in chemical and biological systems. Here, the intramolecular resonant absorption of polarized mid-infrared pulses by bulk water and surface water is investigated using molecular dynamics simulation. The consequent heating based on the OH stretching vibrations is found to be very prompt, achieving more than 100 K temperature jump under irradiation of a pulse with 1 ps width and maximum intensity of 0.5 V/nm. A general anisotropic phenomenon is manifested as a result of preferential resonant excitation of symmetric or asymmetric OH stretching vibration, depending on the relationships between the orientations of water molecules and the polarized direction of the pulse. In the case of water molecules with the preferred dipole orientation, constrained by applied static electric field or spacial confinement, parallel to the polarized direction of the pulses, the energy absorption is dominated by the symmetric stretching mode (around 99 THz), while in the perpendicular case, the asymmetric stretching mode (around 101 THz) is more efficient. Since orientated water molecules are prevalent in chemical and biological systems, these findings concerning orientation-dependent excitation of intramolecular vibrations are of special significance to understood the energy absorption and transition in relevant biochemical processes., Comment: 6 pages, 5 figures

The highly efficient, easy-to-implement, long-ranged and non-destructive way to realize active pumping has been still a great challenge. Here, using molecular dynamics simulations, terahertz electromagnetic wave (TEW) is firstly employed to stimulate an active pump for water transportation by biasedly irradiated in a (6,6) single-walled carbon nanotube (SWCNT) under no external pressure gradient. It is found that an ultrafast conductivity (up to 9.5 /ns) through the pump around a characteristic frequency of 14 THz. The excellent pumping ability is attributed to the resonance coupling between the TEW and water molecules, in which water molecules can gain considerable energy continuously to break the binding of hydrogen bonds and the spatial symmetry. This proposed TEW-driven pump concept will offer a guide in polar molecule transport through artificial or biological nanochannels, particularly in a controllable, non-contact and large-scale process.

In the relativistic impulse approximation (RIA), we study symmetry potentials and in-medium nucleon-nucleon (NN) cross sections with the Nambu-Jona-Lasinio (NJL) model that features chiral symmetry. The chiral symmetry that plays a fundamental role in the nonperturbative physics in the strong interaction is anticipated to add restrictive effects on the symmetry potentials and in-medium NN cross sections. For comparison, we also perform the study with the usual relativistic mean-field (RMF) model. The numerical results with the NJL and RMF models are similar at saturation density and below, since a priori fit was made to saturation properties. With the increase of nuclear density, the chiral symmetry starts to be restored partially in the NJL model, resulting in the explicit fall of the scalar density. In a large energy span, the symmetry potential acquires a significant rise for the partial restoration of the chiral symmetry, compared to the one with the RMF model. It is found that the in-medium NN cross sections in the RIA with the NJL and RMF models both increase with the density in the energy region interested in this study, whereas those with the NJL model increase sharply as long as a clear chiral symmetry restoration takes place. The different tendency of observables in density can be transmitted to the different energy dependence in the RIA. The NJL model is shown to have characteristic energy-dependent symmetry potentials and NN cross sections beyond saturation point, apart from the RMF models.

It is very difficult for any nuclear model to pin down the saturation property and high-density equation of state (EOS) simultaneously because of high nonlinearity of the nuclear many-body problem. In this work, we propose, for the first time, to use the special property of light kaonic nuclei to characterize the relation between saturation property and high-density EOS. With a series of relativistic mean-field models, this special property is found to be the level inversion between orbitals $2S_{1/2}$ and $1D_{5/2}$ in light kaonic nuclei. This level inversion can serve as a theoretical laboratory to group the incompressibility at saturation density and the EOS at supra-normal densities simultaneously., Comment: 10 pages, 4 figures

A sensitive correlation between the ground-state properties of light kaonic nuclei and the symmetry energy at high densities is constructed under the framework of relativistic mean-field theory. Taking oxygen isotopes as an example, we see that a high-density core is produced in kaonic oxygen nuclei, due to the strongly attractive antikaon-nucleon interaction. It is found that the $1S_{1/2}$ state energy in the high-density core of kaonic nuclei can directly probe the variation of the symmetry energy at supranormal nuclear density, and a sensitive correlation between the neutron skin thickness and the symmetry energy at supranormal density is established directly. Meanwhile, the sensitivity of the neutron skin thickness to the low-density slope of the symmetry energy is greatly increased in the corresponding kaonic nuclei. These sensitive relationships are established upon the fact that the isovector potential in the central region of kaonic nuclei becomes very sensitive to the variation of the symmetry energy. These findings might provide another perspective to constrain high-density symmetry energy, and await experimental verification in the future., Comment: 9 pages, 5 figures

The heating effect of terahertz pulse with various frequencies and intensities on the heavy water solution is investigated using the molecular dynamics simulation. Resonant absorptions are found for both heavy water and light water, but at a different resonant frequency which is about 16 THz for heavy water and 21 THz for light water. This resonant phenomenon can be explained perfectly by the collective rotational modes that may release water molecules from hydrogen bonding. The findings not only illustrate the heating mechanism of heavy water solution under the terahertz pulse irradiation, but also demonstrate a novel difference between light water and heavy water that could have potential applications., Comment: 12 pages, 4 figures

It has been a puzzle whether quarks may exist in the interior of massive neutron stars, since the hadron-quark phase transition softens the equation of state (EOS) and reduce the neutron star (NS) maximum mass very significantly. In this work, we consider the light U-boson that increases the NS maximum mass appreciably through its weak coupling to fermions. The inclusion of the U-boson may thus allow the existence of the quark degrees of freedom in the interior of large mass neutron stars. Unlike the consequence of the U-boson in hadronic matter, the stiffening role of the U-boson in the hybrid EOS is not sensitive to the choice of the hadron phase models. In addition, we have also investigated the effect of the effective QCD correction on the hybrid EOS. This correction may reduce the coupling strength of the U-boson that is needed to satisfy NS maximum mass constraint. While the inclusion of the U-boson also increases the NS radius significantly, we find that appropriate in-medium effects of the U-boson may reduce the NS radii significantly, satisfying both the NS radius and mass constraints well., Comment: 18 pages, 7 figures

In this work, we adopt the Nambu-Jona-Lasinio (NJL) model that ensures the nuclear matter saturation properties to study the density dependence of the symmetry energy. With the interactions constrained by the chiral symmetry, the symmetry energy shows novel characters different from those in conventional mean-field models. First, the negative symmetry energy at high densities that is absent in relativistic mean-field (RMF) models can be obtained in the RMF approximation by introducing a chiral isovector-vector interaction, although it would be ruled out by the neutron star (NS) stability. Second, with the inclusion of the isovector-scalar interaction the symmetry energy exhibits a general softening at high densities even for the large slope parameter of the symmetry energy. The NS properties obtained in the present NJL model can be in accord with the observations. The NS maximum mass obtained with various isovector-scalar couplings and momentum cutoffs is well above the $2M_\odot$, and the NS radius obtained well meets the limits extracted from recent measurements. In particular, the significant reduction of the canonical NS radius occurs with the moderate decrease of the slope of the symmetry energy., Comment: 7pages,5figures

Using molecular dynamics simulations, we investigate systematically the water permeation properties across the single-walled carbon nanotube (SWCNT) in the presence of the terahertz electric field (TEF). With the TEF normal to the nanotube, the fracture of the hydrogen bonds results in the giant peak of net fluxes across the SWCNT with a three-fold enhancement centered around 14THz. The phenomenon is attributed to the resonant mechanisms, characterized by librational, rotational, and rotation-induced responses of in-tube polar water molecules to the TEF. For the TEF along the symmetry axis of the nanotube, the vortical modes for resonances and consequently the enhancement of net fluxes are greatly suppressed by the alignment of polar water along the symmetry axis, which characterizes the quasi one-dimensional feature of the SWCNT nicely. The resonances of water molecules in the TEF can have potential applications in the high-flux device designs used for various purposes., Comment: to appear in Nanoscalse (2016)

As the experimental data from kaonic atoms and $K^{-}N$ scatterings imply that the $K^{-}$-nucleon interaction is strongly attractive at saturation density, there is a possibility to form $K^{-}$-nuclear bound states or kaonic nuclei. In this work, we investigate the ground-state properties of the light kaonic nuclei with the relativistic mean field theory. It is found that the strong attraction between $K^{-}$ and nucleons reshapes the scalar and vector meson fields, leading to the remarkable enhancement of the nuclear density in the interior of light kaonic nuclei and the manifest shift of the single-nucleon energy spectra and magic numbers therein. As a consequence, the pseudospin symmetry is shown to be violated together with enlarged spin-orbit splittings in these kaonic nuclei., Comment: 15 pages, 7 figures

By assuming that only gravitation exists between dark matter (DM) and normal matter (NM), we study the effects of fermionic DM on the properties of neutron stars using the two-fluid Tolman-Oppenheimer-Volkoff formalism. It is found that the mass-radius relationship of the DM admixed neutron stars (DANSs) depends sensitively on the mass of DM candidates, the amount of DM, and interactions among DM candidates. The existence of DM in DANSs results in a spread of mass-radius relationships that cannot be interpreted with a unique equilibrium sequence. In some cases, the DM distribution can surpass the NM distribution to form DM halo. In particular, it is favorable to form an explicit DM halo, provided the repulsion of DM exists. It is interesting to find that the difference in particle number density distributions in DANSs and consequently in star radii caused by various density dependencies of nuclear symmetry energy tends to disappear as long as the repulsion of accumulated DM is sufficient. These phenomena indicate that the admixture of DM in neutron stars can significantly affect the astrophysical extraction of nuclear equation of state by virtue of neutron star measurements. In addition, the effect of the DM admixture on the star maximum mass is also investigated., Comment: to be published in Phys. Rev. C (2014)

We study the trend of the nuclear symmetry energy in relativistic mean-field models with appearance of the hyperon and quark degrees of freedom at high densities. On the pure hadron level, we focus on the role of $\Lambda$ hyperons in influencing the symmetry energy both at given fractions and at charge and chemical equilibriums. The softening of the nuclear symmetry energy is observed with the inclusion of the $\Lambda$ hyperons that suppresses the nucleon fraction. In the phase with the admixture of quarks and hadrons, the equation of state is established on the Gibbs conditions. With the increase of the quark volume fraction in denser and denser matter, the apparent nuclear symmetry energy decreases till to disappear. This softening would have associations with the observations which need detailed discriminations in dense matter with the admixture of new degrees of freedom created by heavy-ion collisions.

The stability condition of Landau Fermi liquid theory may be broken when the interaction between particles is strong enough. In this case, the ground state is reconstructed to have a particle distribution different from the Fermi-step function. For specific instances, one case with the vector boson exchange and another with the relativistic heavy-ion collision are taken into consideration. With the vector boson exchange, we find that the relative weak interaction strength can lead to the ground-state rearrangement as long as the fermion mass is large enough. It is found that the relativistic heavy-ion collision may also cause the ground-state rearrangement, affecting the statistics of the collision system., Comment: 9 pages, 2 figures, 3 tables