Physics - Chemical Physics Publications (50)


Physics - Chemical Physics Publications

Nano-crystalline diamond is a new carbon phase with numerous intriguing physical and chemical properties and applications. Small doped nanodiamonds for example do find increased use as novel quantum markers in biomedical applications. However, growing doped nanodiamonds below sizes of 5 nm with controlled composition has been elusive so far. Read More

For a given many-electron molecule, it is possible to define a corresponding one-electron Schr\"odinger equation, using potentials derived from simple atomic densities, whose solution predicts fairly accurate molecular orbitals for single- and multi-determinant wavefunctions for the molecule. The energy is not predicted and must be evaluated by calculating Coulomb and exchange interactions over the predicted orbitals. Potentials are found by minimizing the energy of predicted wavefunctions. Read More

The interface formation between copper phthalocyanine (CuPc) and two representative metal substrates, i.e., Au and Co, was investigated by the combination of ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy. Read More

Zero field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through common techniques, and are often inferred from magnetism data or from high-field electron paramagnetic resonance (EPR) experiments. Here we demonstrate a simple tabletop experimental setup that enables direct and reliable determination of ZFS parameters at variable temperature. Read More

As one of the simple alkali metals, sodium has been of fundamental interest for shock physics experiments, but knowledge of its equation of state (EOS) in hot, dense regimes is not well known. By combining path integral Monte Carlo (PIMC) results for partially-ionized states [B. Militzer and K. Read More

Diffusion quantum Monte Carlo calculations with partial and full optimization of the guide function are carried out for the dissociation of the FeS molecule. It is demonstrated that agreement with experiment is obtained only after energy optimization of the orbitals of a complete active space wave function in the presence of a Jastrow correlation function. Furthermore, it is shown that orbital optimization leads to a $^5\Delta$ ground state, in agreement with experiments, but in disagreement with high-level ab initio calculations predicting a $^5\Sigma^+$ ground state. Read More

We present a comprehensive benchmark study of the adsorption energy of a single water molecule on the (001) LiH surface using periodic coupled cluster and quantum Monte Carlo theories. We benchmark and compare different implementations of quantum chemical wave function based theories in order to verify the reliability of the predicted adsorption energies and the employed approximations. Furthermore we compare the predicted adsorption energies to those obtained employing widely-used van der Waals density-functionals. Read More

Ion hydrations are ubiquitous in natural and fundamental processes. A quantitative analysis of a novel CO2 sorbent driven by ion hydrations was presented by molecular dynamics (MD). We explored the humidity effect on the diffusion and structure of ion hydrations in CO2 sorbent, as well as the working mechanism of the moisture-swing CO2 sorbent. Read More

We develop a new scheme for determining molecular partial atomic charges (PACs) with external electrostatic potential (ESP) closely mimicking that of the molecule. The PACs are the "minimal corrections" to a reference-set of PACs necessary for reproducing exactly the tensor components of the Cartesian zero- first- and second- molecular electrostatic multipoles. We evaluate the quality of ESP reproduction when "minimally correcting" (MC) Mulliken, Hirshfeld or iterated-Hirshfeld reference PACs. Read More

The intermediate state dependence of photoelectron circular dichroism (PECD) in resonance-enhanced multi-photon ionization of fenchone in the gas phase is experimentally studied. By scanning the excitation wavelength from 359 to 431 nm we simultaneously excite up to three electronically distinct resonances. In the PECD experiment performed with a broadband femtosecond laser their respective contributions to the photoelectron spectrum can be resolved. Read More

We use accurate ab initio and quantum scattering calculations to explore the prospects for sympathetic cooling of the heavy molecular radical SrOH($^2\Sigma$) by ultracold Li atoms in a magnetic trap. A two-dimensional potential energy surface (PES) for the triplet electronic state of Li-SrOH is calculated ab initio using the partially spin-restricted coupled cluster method with single, double and perturbative triple excitations and a large correlation-consistent basis set. The highly anisotropic PES has a deep global minimum in the skewed Li-HOSr geometry with $D_e=4932$ cm$^{-1}$ and saddle points in collinear configurations. Read More

High-throughput computational screening has emerged as a critical component of materials discovery. Direct density functional theory (DFT) simulation of inorganic materials and molecular transition metal complexes is often used to describe subtle trends in inorganic bonding and spin-state ordering, but these calculations are computationally costly and properties are sensitive to the exchange-correlation functional employed. To begin to overcome these challenges, we trained artificial neural networks (ANNs) to predict quantum-mechanically-derived properties, including spin-state ordering, sensitivity to Hartree-Fock exchange, and spin- state specific bond lengths in transition metal complexes. Read More

Cytosine methylation has been found to play a crucial role in various biological processes, including a number of human diseases. The detection of this small modification remains challenging. In this work, we computationally explore the possibility of detecting methylated DNA strands through direct electrical conductance measurements. Read More

We investigate the impact of choosing regressors and molecular representations for the construction of fast machine learning (ML) models of thirteen electronic ground-state properties of organic molecules. The performance of each regressor/representation/property combination is assessed with learning curves which report approximation errors as a function of training set size. Molecular structures and properties at hybrid density functional theory (DFT) level of theory used for training and testing come from the QM9 database [Ramakrishnan et al, Scientific Data 1 140022 (2014)] and include dipole moment, polarizability, HOMO/LUMO energies and gap, electronic spatial extent, zero point vibrational energy, enthalpies and free energies of atomization, heat capacity and the highest fundamental vibrational frequency. Read More

The Donnan model describes the electric double layer structure inside carbon micropores and is an essential element of larger-scale models for capacitive and Faradaic porous carbon electrodes for energy storage and water desalination. The Donnan model was not yet developed to describe the expansion of carbon electrodes upon charging. Here we provide a simple theory which predicts that the one-dimensional expansion of a carbon particle scales with electrode charge density according to a 4/3$^\text{rd}$ power. Read More

We report here the results of Molecular Dynamics simulations of the drift mobility of negative oxygen ions in very dense neon gas in the supercritical phase. The simulations relatively well reproduce the trend of the experimental data. The rationalization of the mobility behavior as a function of the gas density is given in terms of the number of atoms correlated in the first solvation shell around the ion. Read More

We show how to emulate a conventional pump-probe scheme using a single frequency-chirped ultrashort UV pulse to obtain a time-resolved image of molecular ultrafast dynamics. The chirp introduces a spectral phase in time that encodes the delay between the pump and the probe frequencies contained in the pulse. By comparing the results of full dimensional ab initio calculations for the H$^+_2$ molecule with those of a simple sequential model, we demonstrate that, by tuning the chirp parameter, two-photon energy-differential ionization probabilities directly map the wave packet dynamics generated in the molecule. Read More

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for coarse grained models of electrolyte solution. Here, we provide rigorous definitions of the various types of single ion solvation free energies based on different simulation protocols. Read More

The strong-interaction limit of the Hohenberg-Kohn functional defines a multimarginal optimal transport problem with Coulomb cost. From physical arguments, the solution of this limit is expected to yield strictly-correlated particle positions, related to each other by co-motion functions (or optimal maps), but the existence of such a deterministic solution in the general three-dimensional case is still an open question. A conjecture for the co-motion functions for radially symmetric densities was presented in Phys. Read More

The reaction ensemble and the constant pH method are well-known chemical equilibrium approaches to simulate protonation and deprotonation reactions in classical molecular dynamics and Monte Carlo simulations. In this article, we show similarity between both methods {under certain conditions}. We perform molecular dynamics simulations of a weak polyelectrolyte in order to compare the titration curves obtained by both approaches. Read More

A general theoretical framework is derived for the recently developed multi-state trajectory (MST) approach from the time dependent Schr\"odinger equation, resulting in equations of motion for coupled nuclear-electronic dynamics equivalent to Hamilton dynamics or Heisenberg equation based on a new multistate Meyer-Miller (MM) model. The derived MST formalism incorporates both diabatic and adiabatic representations as limiting cases, and reduces to Ehrenfest or Born-Oppenheimer dynamics in the mean field or the single state limits, respectively. By quantizing nuclear dynamics to a particular active state, the MST algorithm does not suffer from the instability caused by the negative instant electronic population variables unlike the standard MM dynamics. Read More

We demonstrate that 4-body real space Jastrow factors are, with the right type of Jastrow basis function, capable of performing successful wave function stenciling to remove unwanted ionic terms from an overabundant fermionic reference without unduly modifying the remaining components. In addition to greatly improving size consistency (restoring it exactly in the case of a geminal power), real-space wave function stenciling is, unlike its Hilbert space predecessors, immediately compatible with diffusion Monte Carlo, allowing it to be used in the pursuit of compact, strongly correlated trial functions with reliable nodal surfaces. We demonstrate the efficacy of this approach in the context of a double bond dissociation by using it to extract a qualitatively correct nodal surface despite being paired with a restricted Slater determinant, that, due to ionic term errors, produces a ground state with a qualitatively incorrect nodal surface when used in the absence of the Jastrow. Read More

Molecules are the most demanding quantum systems to be simulated by quantum computers because of their complexity and the emergent role of quantum nature. The recent theoretical proposal of Huh et al. (Nature Photon. Read More

Ionic solutions are often regarded as fully dissociated ions dispersed in a polar solvent. While this picture holds for dilute solutions, at higher ionic concentrations, oppositely charged ions can associate into dimers, referred to as Bjerrum pairs. We consider the formation of such pairs within the nonlinear Poisson-Boltzmann framework, and investigate their effects on bulk and interfacial properties of electrolytes. Read More

Energy has always been the driving force in the technological and economic development of societies. The consumption of a significant amount of energy is required to provide basic living conditions of developed countries (heating, transportation, lighting, etc.). Read More

Quantum chemical calculations have been used to study several reactions leading to the formation of mono-(H$_2$MBP), di-(HDBP) and tributyl-phosphate (TBP) in gas and liquid phases. The energies were calculated using local coupled cluster with single and double excitation operators and perturbative treatment of triple excitations [LCCSD(T)], extrapolated to the complete basis set limit to minimize uncertainties from the basis set and electron correlation effects. Solvation enthalpies are computed with the conductor like screening model for real solvents [COSMO-RS], for which we can estimate an uncertainty of less that 10 kJ mol$^{-1}$. Read More

The mathematical foundation of the so-called extended coupled-cluster method for the solution of the many-fermion Schr\"odinger equation is here developed. We prove an existence and uniqueness result, both in the full infinite-dimensional amplitude space as well as for discretized versions of it. The extended coupled-cluster method is formulated as a critical point of an energy function using a generalization of the Rayleigh-Ritz principle: the bivariational principle. Read More

We present a method which allows for the extraction of physical quantities directly from zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) data. A numerical density matrix evolution is used to simulate ZULF NMR spectra of several molecules in order to fit experimental data. The method is utilized to determine the indirect spin-spin couplings ($J$-couplings) in these, which is achieved with precision of $10^{-2}$--$10^{-4}$ Hz. Read More

We present a theoretical analysis of the entanglement entropy of an open dimer, such as a photosynthetic biological system of two excited states of chlorophyll molecules interacting with a protein-solvent environment, modeled by a field of oscillators. We show that the entanglement entropy of the chlorophyll dimer is generated by its decoherence, caused by the environment interaction. Depending on the type of interaction, not all environment oscillators carry significant entanglement entropy. Read More

Affiliations: 1Istituto di Chimica dei Composti Organometallici, 2Istituto di Chimica dei Composti Organometallici, 3Istituto di Chimica dei Composti Organometallici, 4Istituto di Chimica dei Composti Organometallici, 5Istituto di Chimica dei Composti Organometallici, 6Istituto di Chimica dei Composti Organometallici, 7Istituto di Chimica dei Composti Organometallici, 8Istituto di Chimica dei Composti Organometallici

Polystyrene-based phosphorene nanocomposites were prepared by a solvent blending procedure allowing the embedding of black phosphorus (BP) nanoflakes in the polymer matrix. Raman spectroscopy, X Ray Diffraction and TEM microscopy were employed to characterize the structural and the morphological characteristics of the achieved hybrids, with the aim to evaluate the dispersion level of black phosphorus layers. TGA, DSC analysis as well as thermal oxidation and photo-degradation techniques were employed to investigate the thermal- and the photo-stability of the samples. Read More

The PAH family of organic compounds (polycyclic aromatic hydrocarbons), involved in several fields of chemistry, has received particular attention in astrochemistry, where their vibrational spectroscopy, thermodynamic, dynamic, and fragmentation properties are now abundantly documented. This survey aims at drawing trends for low spin-multiplicity surfaces of PAHs bearing internal energies in the range 1-10 eV. It addresses some typical alternatives to the ground-state regular structures of PAHs, making explicit possible intramolecular rearrangements leading to high-lying minima. Read More

The development of semilocal models for the kinetic energy density (KED) is an important topic in density functional theory (DFT). This is especially true for subsystem DFT, where these models are necessary to construct the required non-additive embedding contributions. In particular, these models can also be efficiently employed to replace the exact KED in meta-Generalized Gradient Approximation (meta-GGA) exchange-correlation functionals allowing to extend the subsystem DFT applicability to the meta-GGA level of theory. Read More

We have used laser ablation and helium buffer-gas cooling to produce the titanium-helium van der Waals molecule at cryogenic temperatures. The molecules were detected through laser-induced fluorescence spectroscopy. Ground-state Ti-He binding energies were determined for the ground and first rotationally excited states from studying equilibrium thermodynamic properties, and found to agree well with theoretical calculations based on newly calculated ab initio Ti-He interaction potentials, opening up novel possibilities for studying the formation, dynamics, and non-universal chemistry of van der Waals clusters at low temperatures. Read More

Reactivity of the [FeO]2+ group in the abstraction of hydrogen from methane is determined by metastable oxyl state FeIII-O* causing the negative spin polarization of the methyl moiety as was shown by quantum-chemical means with the use of model iron hydroxide species FeO(OH)2, Fe2O(OH)5, and Fe4O5(OH)3 as an example. Read More

Several active areas of research in novel energy storage technologies, including three-dimensional solid state batteries and passivation coatings for reactive battery electrode components, require conformal solid state electrolytes. We describe an atomic layer deposition (ALD) process for a member of the lithium phosphorus oxynitride (LiPON) family, which is employed as a thin film lithium-conducting solid electrolyte. The reaction between lithium tert-butoxide (LiO$^t$Bu) and diethyl phosphoramidate (DEPA) produces conformal, ionically conductive thin films with a stoichiometry close to Li$_2$PO$_2$N between 250 and 300$^\circ$C. Read More

Metal-support interactions are frequently invoked to explain the enhanced catalytic activity of metal nanoparticles dispersed over reducible metal-oxide supports, yet the atomic scale mechanisms are rarely known. Here, we use scanning tunneling microscopy to study a Pt1-6/Fe3O4 model catalyst exposed to CO, H2, O2, and mixtures thereof, at 550 K. CO extracts lattice oxygen at the cluster perimeter to form CO2, creating large holes in the metal-oxide surface. Read More

We present analytical solutions to a quantum-mechanical three-body problem in three dimensions, which describes a helium-like two-electron atom. Similarly to Hooke's atom, the Coulombic electron-nucleus interaction potentials are replaced by harmonic potentials. The electron-electron interaction potential is taken to be both screened (decaying faster than the inverse of the interparticle separation) and regularized (in the limit of zero separation). Read More

Recognized as important interstellar constituents, polycyclic aromatic hydrocarbons (PAHs) have been intensively studied in astrochemistry and their spectroscopy, thermodynamics, dynamics, and fragmentations are now amply documented. There exists typical alternatives to the ground-state regular planar structures of PAHs, as long as they bear internal energies in the range 1-10 eV. Resulting from intramolecular rearrangements, such high-lying minima on the potential- energy surfaces should be taken into consideration in the studies of PAH processing in astrophysical conditions. Read More

Few inventions have shaped the world like the incandescent bulb. While Edison used thermal radiation from ohmically heated conductors, some noble metals exhibit "cold" electroluminescence (EL) in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennae, or scanning-tunnelling microscopy (STM). The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Read More

We introduce a hybrid approach to applying the density matrix renormalization group (DMRG) to continuous systems, combining a grid approximation along one direction with a finite Gaussian basis set along the remaining two directions. This approach is especially useful for chain-like molecules, where the grid is used in the long direction, and we demonstrate the approach with results for hydrogen chains. The computational time for this system scales approximately linearly with the length of the chain, as we demonstrate with minimal basis set calculations with up to 1000 atoms, which are near-exact within the basis. Read More

Potassium (K) intercalated manganese phthalocyanine (MnPc) reveals vast changes of its electronic states close to the Fermi level. However, theoretical studies are controversial regarding the electronic configuration. Here, MnPc doped with K was studied by ultraviolet, X-ray, and inverse photoemission, as well as near edge X-ray absorption fine structure spectroscopy. Read More

Random phase approximation ground state contains electronic configurations where two (and more) identical electrons can occupy the same molecular spin-orbital in apparent violation of the Pauli exclusion principle. This unphysical overcounting of electronic configurations happens due to quasiboson approximation in the treatment of electron-hole pair creation and annihilation operators. We describe the method to restore the Pauli principle in the random phase approximation wavefunction and obtain the corrections to expressions for molecular observables. Read More

We measure the homogeneous excitation linewidth of regioregular poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by means of two-dimensional coherent photoluminescence excitation spectroscopy. At a temperature of 8\,K, we find a linewidth that is always $\gtrsim 110$\,meV full-width-at-half-maximum, which is a significant fraction of the total linewidth. It displays a spectral dependence and is minimum near the 0--0 origin peak. Read More

We perform a static analysis of a circular cylinder laying at a liquid$-$gas interface and acting as a barrier between a surfactant-free surface and a surfactant-loaded surface. The respective surfaces have uniform surface tensions $\gamma_a$ and $\gamma_b$ that generate a surface tension imbalance $\Delta \gamma = \gamma_a - \gamma_b$. In addition to determining the general implications of the balances for forces and torques, we quantify how $\Delta \gamma$ influences the maximum load-bearing capacity of a floating cylinder for a specific set of parameters. Read More

The present paper introduces a new multi-reference perturbation approach developed at second order, based on a Jeziorsky-Mokhorst expansion using individual Slater determinants as perturbers. Thanks to this choice of perturbers, an effective Hamiltonian may be built, allowing for the dressing of the Hamiltonian matrix within the reference space, assumed here to be a CAS-CI. Such a formulation accounts then for the coupling between the static and dynamic correlation effects. Read More

Accurate prediction of the electronic and hydrogen storage properties of linear carbon chains (Cn) and Li-terminated linear carbon chains (Li2Cn), with n carbon atoms (n = 5 - 10), has been very challenging for traditional electronic structure methods, due to the presence of strong static correlation effects. To meet the challenge, we study these properties using our newly developed thermally-assisted-occupation density functional theory (TAO-DFT), a very efficient electronic structure method for the study of large systems with strong static correlation effects. Owing to the alteration of the reactivity of Cn and Li2Cn with n, odd-even oscillations in their electronic properties are found. Read More

FeRh is a showcase for caloric materials genome, transforming upon heating from the type-2 antiferromagnet (AFM) to a ferromagnet (FM). FeRh AFM (but not FM) cubic B2 lattice is unstable at ambient pressure. We describe the stable orthorhombic AFM FeRh structure at low temperature T. Read More

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical/NIR pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by attosecond transient absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium M_{4,5}-edge (~30 eV). Read More

The hydration of ions in nanoscale hydrated clusters is ubiquitous and essential in many physical and chemical processes. Here we show that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules is investigated by ab initio method. Read More