Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L26: Advances in Density Functional Theory and Applications |
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Sponsoring Units: DCP Chair: Spiridoula Matsika, Temple University Room: 289 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L26.00001: Spin-state energetics of Fe complexes from an optimally-tuned range-separated hybrid functional Georgia Prokopiou, Leeor Kronik We assess whether the optimally-tuned range separated hybrid (OT-RSH) functional approach can predict the correct ground-state electronic configuration and spin-state energetics of complexes that can potentially exhibit multiple spin configurations. To that end, we investigate eight iron complexes: Four spin-crossover complexes, for which reference data from other approximate density functionals are available, and four smaller complexes, for which reference \textit{ab initio} data are available. \newline We show that the spin-state energetics are mostly governed by the percentage of short-range exact exchange and are only weakly influenced by the choice of range-separation parameter. However, the electronic structure, especially the HOMO-LUMO gap, is much more sensitive to the range-separation parameter. We find that use of OT-RSH improves the electronic structure, as compared with that obtained from semi-local or global hybrid density functionals. However, as with global hybrid functionals, correct prediction of the ground-state in the spin-crossover compounds requires a reduction in the amount of short-range exact exchange, possibly owing to a larger role of static correlation. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L26.00002: High throughput optimization of Fermi-orbital descriptors Der-You Kao, Koblar Jackson The innovative Fermi-L\”{o}wdin-orbital self-interaction correction (FLO-SIC) to density functional theory (DFT) \footnote{ M. R. Pederson, A. Ruzsinszky, and J. P. Perdew, J. Chem. Phys. \textbf{140},121103 (2014).} uses N spatial points known as Fermi-orbital descriptors (FOD’s) to define a unitary transformation between the canonical Kohn-Sham orbitals and the local orbitals used to compute the DFT-SIC total energy. In this talk we describe a simple, unbiased method for optimizing these positions. It involves creating a large number of independent random starting arrangements and then performing a separate local optimization of the FOD positions for each, using derivatives of the total energy with respect to the FOD positions, i.e. FOD “forces”.\footnote{M. R. Pederson, J. Chem. Phys. \textbf{142}, 064112 (2015).} A good approximation of the optimal positions can be found by carrying out the local optimization on a frozen space of occupied orbitals. After the approximate positions are found, the occupied orbital space and FODs can be further optimized in tandem to minimize E$^{DFT-SIC}$. Results of using this approach for the Cr atom and Cr$_{2}$ will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L26.00003: Modeling of the exact exchange derivative discontinuity in semi-local potentials Alexander Lindmaa, Rickard Armiento The derivative discontinuity (DD), i.e., the abrupt constant shift of the exchange-correlation potential at integer particle numbers plays a crucial role in Kohn-Sham density-functional theory (KS DFT). It is needed to determine the fundamental gap of a system, and is, e.g, related to obtaining an adequate description of charge transfer. While usual semi-local approximations give good results for properties related to the total energy, they do not in general possess a DD. A recently proposed semi-local exchange functional, AK13 [1], mimics features related to the DD by a discontinuous change of its asymptote upon adding a fraction of an electron through an integer. This is because its potential depends asymptotically on the highest occupied KS eigenvalue. In this work we investigate the behavior of the DD in exact exchange (EXX) within the optimized effective potential (OEP) method for simple systems such as spherically symmetric atoms. We compare with the general behavior that results from the AK13 construction, and other alternatives. We discuss some challenges related to describing the EXX DD correctly in future development of semi-local functionals based on the AK13 construction. [1] Phys. Rev. Lett. 111, 036402 (2013) [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L26.00004: Generalized Gradient Approximation for Exchange-Correlation Free Energy Valentin Karasiev, James Dufty, Samuel Trickey The exchange-correlation (XC) free-energy is an essential ingredient of density functional theory (DFT). Use of a ground-state functional completely misses the explicit T-dependence. Depending on state conditions, that dependence can be important for warm dense matter (WDM)[2]. The local density approximation [1] XC free-energy functional has the proper T-dependence for the homogeneous electron gas. Here we analyze the finite-T gradient corrections for the X and C contributions to identify the appropriate T-dependent dimensionless density gradient variables. We then introduce a generalized gradient approximation (GGA) for the XC free energy with correct limits [3]. The result, together with the VT84F finite T GGA for the non-interacting free energy [4] provides a non-empirical GGA free-energy functional for WDM. 1. V.V. Karasiev, T. Sjostrom, J. Dufty, and S.B. Trickey, Phys. Rev. Lett. 112, 076403 (2014). 2. V.V. Karasiev, L. Calderin, and S.B. Trickey, Phys. Rev. E 93, 063207 (2016). 3. V.V. Karasiev, J. Dufty, and S.B. Trickey, manuscript in preparation. 4. V.V. Karasiev, D. Chakraborty, O.A. Shukruto, and S.B. Trickey, Phys. Rev. B 88, 161108(R) (2013). [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L26.00005: Towards a kinetic energy density functional for the water molecule Omololu Akin-Ojo, Doyin Shittu Development of an accurate kinetic energy kinetic energy density functional (KEDF) is a holy grail. In this work, local KEDFS are parameterized for the water molecule in order to reproduce Kohn-Sham density functional theory (KS-DFT) results. Energies, forces and dipole moments from these KEDFs are presented. Problems with the convergence of the self-consistent-field (SCF) calculations are discussed together with possible solutions. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L26.00006: General degeneracy in density functional perturbation theory Mark Palenik, Brett Dunlap Degenerate perturbation theory from quantum mechanics is inadequate in density functional theory (DFT) because of nonlinearity in the Kohn-Sham (KS) potential. We develop the fully general degenerate DFT perturbation theory. The requirement that a differentiable map connects the unperturbed state to the perturbed state defines the unitary transformations and changes in Fermi-level occupation numbers at each order. The resulting methodology is applied to the iron atom ground state, which displays 3$d$-4$s$ degeneracy, calculated with the VWN functional. By applying a perturbing quadrupole field, we demonstrate how the equations for the first-order density and first through third-order energies can be solved in a system where degeneracy appears both due to symmetry requirements and accidentally, between different representations of the symmetry group. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L26.00007: Stacking van der Waals materials Predrag Lazic We have developed a code (CellMatch [1]) that searches for common unit cells of two layered structures. Typically the two structures will not have a common lattice constant so a compromise is needed between the size of the cell and the strain imposed on one of the structures. Whether it is a heterostructure of two van der Waals materials or a vdW material on a substrate CellMatch searches through possible common unit cells yielding a strain for each result. We demonstrate the use of the code in combination with Density Functional Theory calculations - by studying cases of MoS2 growth on the sapphire surface, and hBN on the Ir(111). [1] P. Lazic, Comput. Phys. Comm. \textbf{197}, 324 (2015). [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L26.00008: Adsorption of TNT, DNAN, NTO, FOX7 and NQ onto Cellulose, Chitin and Cellulose Triacetate. Insights from Density Functional Theory Calculations Guido Todde, Sanjiv Jha, Gopinath Subramanian, Manoj Shukla Insensitive munitions (IM) like DNAN (2,4-dinitroanisole), NTO (3-nitro-1,2,4-triazol-5-one), NQ (nitroguanidine) and FOX7 (1,1-diamino-2,2-dinitroethene) reduce the risk of accidental explosions due to shock and high temperature exposure. These compounds are used as replacement for TNT (2,4,6-trinitromethylbenzene) and RDX (1,3,5-hexahydro-1,3,5-trinitro-1,3,5-triazine). Unfortunately they are more soluble than TNT or RDX, hence they can easily spread in the environment and get dissolved by precipitation. Due to the abundance of cellulosic biomass in the environment it is important to investigate the adsorption of these new contaminants onto cellulose and cellulose derivative surfaces. Using Density Functional Theory methods we have studied the adsorption of TNT, DNAN, NTO, NQ and FOX7 onto cellulose I$\alpha$ and I$\beta$, chitin and cellulose triacetate. The solvent effect on the adsorption was also investigated. Our results show how all contaminants are adsorbed onto chitin and cellulose I$\alpha$. FOX7 is very weakly absorbed onto cellulose I$\beta$ which is mainly found in wood and ramie fibers. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L26.00009: Ab-initio studies of nitrogen-vacancy impurity complexes in diamond Alejandro Gallo, Andreas Grüneis Nitrogen Vacancy defects in diamond have become over the last years an important candidate for a bulk room temperature quantum information processing device. We investigate the feasibility of calculating properties such as inter-system crossings between triplet and singlet levels, spin-spin interaction parameters and deformation tensors using state-of-the-art ab-initio techniques. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L26.00010: The stability of DOTA-chelated radiopharmaceuticals within $^{225}$Ac decay pathway studied with density functional theory. Aleksandra Karolak, Artem Khabibullin, Mikalai Budzevich, M. Martinez, Michael Doliganski, Mark McLaughlin, Lilia Woods, David Morse Ligand structures encapsulating metal ions play a central role as contrast agents in Magnetic Resonance Imaging (MRI) or as agents delivering toxic cargo directly to tumor cells in targeted cancer therapy. The structural stability and interaction with solutions of such complexes are the key elements in understanding the foundation of delivery process. We present a comparative study for the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelated to radioactive isotopes of $^{225}$Ac, $^{221}$Fr, $^{217}$At, $^{213}$Bi and a control $^{68}$Gd. Using density functional theory methods we investigate the structural stability of complexes for cancer therapy including binding energies, charge transfer, electron densities. The van der Waals interactions are included in the simulations to take into account weak dispersion forces present in such structures. Our results reveal that Ac-DOTA, Bi-DOTA and Gd-DOTA are the most stable complexes in the group. We also show that the water environment is a key ingredient for the structural coordination of the DOTA structures. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L26.00011: Stability of Finite Subspaces in Density Functional Theory: Application to Simple Atoms P. Iza, F.J. Torres, E. V. Lude\~na, Y. Carrillo, L. Rinc\'on, D. Zambrano The validity of the first Hohenberg-Kohn theorem, namely the one-to-one relationship between an external potential and the one-particle density, is examined; when it is applied to finite subspaces and consider the stability of these subspaces with respect to external potentials. This is done by analyzing the DFT description of some atoms (e.g., H, He, Li and Be) provided by the solution of the Kohn-Sham equation in a finite Gaussian basis set. We show that in the finite subspace generated from the finite basis set, it is possible to construct external potentials that differ from one another by more than a constant but which associate with the same one-particle density. We carry out the specific construction of these potentials for the above atoms using the wave functions resulting from the application of the B3LYP functional. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L26.00012: Tuning the band structures of self-activated luminescence materials for white- emission and biological application. Junying Zhang The properties of the self-activated luminescence materials depend closely on the point defects, crystal size and even shape. Using first-principles calculation, we exploit the influence of oxygen vacancy on the band structure of monoclinic Y$_{2}$WO$_{6}$ . Then by controlling the calcining process and doping with some rare earth elements, strong green emission and also white-emission could be achieved under long-wavelength violet light irradiation. For graphitic- phase C$_{3}$N$_{4}$ (g-C$_{3}$N$_{4})$, bright blue emission was obtained by delamination of the bulk materials and reducing the crystal size. By further reducing the particle to about 5nm, water-dispersible g-C$_{3}$N$_{4}$ quantum dots were produced which show potential application as photodynamic therapy agent. The pH-sensitive emission of g-C$_{3}$N$_{4}$ deduces the high cytotoxicity to cancer cell and low cytotoxicity to the normal cell of g-C$_{3}$N$_{4}$-porphyrin. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L26.00013: Visualizing Chemical Bonds in Synthetic Molecules Laura C. Collins, Anthony Ruth, David B. Green, Boldizsar Janko, Kenjiro K. Gomes The use of synthetic quantum systems makes it possible to study phenomena that cannot be probed by conventional experiments. We created synthetic molecules using atomic manipulation and directly imaged the chemical bonds using tunneling spectroscopy. These synthetic systems allow us to probe the structure and electronic properties of chemical bonds in molecules, including those that would be unstable in nature, with unprecedented detail. The experimental images of electronic states in our synthetic molecules show a remarkable match to the charge distribution predicted by density functional theory calculations. The statistical analysis of the spectroscopy of these molecules can be adapted in the future to quantify aromaticity, which has been difficult to quantify universally thus far due to vague definitions. We can also study anti-aromatic molecules which are unstable naturally, to illuminate the electronic consequences of antiaromaticity. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L26.00014: Molecules Without Atoms Anthony Ruth, Laura Collins, Kenjiro Gomes, Boldizsar Janko We present a real-space representation of molecules which results in the normal bonding rules and electronic structure of chemistry without atom-centered coulomb potentials. Using a simple mapping, we can generate atomless molecules from the structure of real molecules. Additionally, molecules without atoms show similar covalent bonding energies and transfer of charge in ionic bonds as real molecules. The atomless molecules contain only the valence and conduction electronic structure of the real molecule. Using the framework of the Atoms in Molecules (AIM) theory of Bader, we prove that the topological features of the valence charge distribution of molecules without atoms are identical to that of real molecules. In particular, the charge basins of atomless molecules show identical location and quantities of representative charge. We compare the accuracy, computational cost, and intuition gained from electronic structure calculations of molecules without atoms with the use of pseudopotentials to represent atomic cores in density functional theory. [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L26.00015: Error sources in transition matrix Ising Model calculations David Yevick The relative accuracy of several illustrative implementations of the transition matrix method will be discussed in the context of the two dimensional Ising model. Observed deviations from analytic results will be analyzed heuristically and compared to those associated with alternative techniques. [Preview Abstract] |
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