This article presents a perspective on Kohn-Sham density functional theory (KS-DFT) for electronic structure calculations in chemical physics. This theory is in widespread use for applications to both molecules and solids. We pay special attention to several aspects where there are both concerns and progress toward solutions. These include: 1. The treatment of open-shell and inherently multiconfig-urational systems (the latter are often called multireference systems and are variously classified as having strong correlation, near-degeneracy correlation, or high static correlation; KS-DFT must treat these systems with broken-symmetry determinants). 2. The treatment of noncovalent interactions. 3. The choice between developing new functionals by parametrization, by theoretical constraints, or by a combination. 4. The ingredients of the exchange-correlation functionals used by KS-DFT, including spin densities, the magnitudes of their gradients, spin-specific kinetic energy densities, nonlocal exchange (Hartree-Fock exchange), nonlocal correlation, and subshell-dependent corrections (DFT+U). 5. The quest for a universal functional, where we summarize some of the success of the latest Minnesota functionals, namely MN15-L and MN15, which were obtained by optimization against diverse databases. 6. Time-dependent density functional theory, which is an extension of DFT to treat time-dependent problems and excited states. The review is a snapshot of a rapidly moving field, and-like Marcel Duchamp-we hope to convey progress in a stimulating way. Published by AIP Publishing. [http://dx.

The Earth acts as a gigantic heat engine driven by decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes, and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing to grow the solid inner core, and on chemical convection due to light elements expelled from the liquid on freezing. The power supplied to the geodynamo, measured by the heat-flux across the core-mantle boundary (CMB), places constraints on Earth's evolution 1 . Estimates of CMB heatflux 2-5 depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent difficulties in experimentation and theory. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principlesthe first directly computed values that do not rely on estimates based on extrapolations. The mixtures of Fe, O, S, and Si are taken from earlier work 6 and fit the seismologically-determined core density and inner-core boundary density jump 7,8 . We find both conductivities to be 2-3 times higher than estimates in current use. The changes are so large that core thermal histories and power requirements must be reassessed. New estimates of adiabatic heat-flux give 15-16 TW at the CMB, higher than present estimates of CMB heat-flux based on mantle convection 1 ; the top of the core must be thermally stratified and any convection in the upper core driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted and future models of mantle evolution must incorporate a high CMB heat-flux and explain recent formation of the inner core.First principles calculations of transport properties based on density functional theory (DFT) have been used in the past for a number of materials (e.g. [9,10]). Recently, increased computer power has facilitated simulations of large systems, allowing to completely address the problem of the size of the simulation cell, which for the electrical conductivity (σ) can be a serious one 11 . Here we report a series of calculations of the electrical and thermal conductivity (k) of iron at Earth's core conditions, using DFT. We previously used these methods to compute an extensive number of thermodynamic properties of iron and iron alloys, including the whole melting curve of iron in the pressure range [50-400] GPa 12,13 and the chemical potentials of oxygen, sulphur and silicon in solid and liquid iron at inner core boundary (ICB) conditions, which we used to place constraints on core composition 6 . Recently, we computed the conductivity of iron at ambient conditions, and obtained values in very good agreement with experiments 14 .The calculations of the conductivities were performed at 7 points on the iron and two pos...

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The free energy and other thermodynamic properties of hexagonal-close-packed iron are calculated by direct ab initio methods over a wide range of pressures and temperatures relevant to the Earth's core. The ab initio calculations are based on density-functional theory in the generalisedgradient approximation, and are performed using the projector augmented wave (PAW) approach. Thermal excitation of electrons is fully included. The Helmholtz free energy consists of three parts, associated with the rigid perfect lattice, harmonic lattice vibrations, and anharmonic contributions, and the technical problems of calculating these parts to high precision are investigated. The harmonic part is obtained by computing the phonon frequencies over the entire Brillouin zone, and by summation of the free-energy contributions associated with the phonon modes. The anharmonic part is computed by the technique of thermodynamic integration using carefully designed reference systems. Detailed results are presented for the pressure, specific heat, bulk modulus, expansion coefficient and Grüneisen parameter, and comparisons are made with values obtained from diamond-anvil-cell and shock experiments.PACS numbers: 71.15.-m 64.10.+h 62.50.+p

Ab initio techniques based on density functional theory in the projector-augmented-wave implementation are used to calculate the free energy and a range of other thermodynamic properties of liquid iron at high pressures and temperatures relevant to the Earth's core. The ab initio free energy is obtained by using thermodynamic integration to calculate the change of free energy on going from a simple reference system to the ab initio system, with thermal averages computed by ab initio molecular dynamics simulation. The reference system consists of the inverse-power pair-potential model used in previous work. The liquid-state free energy is combined with the free energy of hexagonal close packed Fe calculated earlier using identical ab initio techniques to obtain the melting curve and volume and entropy of melting. Comparisons of the calculated melting properties with experimental measurement and with other recent ab initio predictions are presented. Experiment-theory comparisons are also presented for the pressures at which the solid and liquid Hugoniot curves cross the melting line, and the sound speed and Grüneisen parameter along the Hugoniot. Additional comparisons are made with a commonly used equation of state for high-pressure/high-temperature Fe based on experimental data.

Water monomer adsorption on graphene is examined with state-of-the-art electronic structure approaches. The adsorption energy determinations on this system from quantum Monte Carlo and the random-phase approximation yield small values of <100 meV. These benchmarks provide a deeper understanding of the reactivity of graphene that may underpin the development of improved more approximate methods enabling the accurate treatment of more complex processes at wet-carbon interfaces. As an example, we show how dispersion-corrected density functional theory, which we show gives a satisfactory description of this adsorption system, predicts that water undergoes ultra-fast diffusion on graphene at low temperatures.

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Density functional theory and quantum Monte Carlo simulations reveal that the structure of the Stone-Wales ͑SW͒ defect in graphene is more complex than hitherto appreciated. Rather than being a simple in-plane transformation of two carbon atoms, out-of-plane wavelike defect structures that extend over several nanometers are predicted. Equivalent wavelike SW reconstructions are predicted for hexagonal boron-nitride and polycyclic aromatic hydrocarbons above a critical size, demonstrating the relevance of these predictions to sp 2-bonded materials in general.