Aliaksandr V. Krukau

Bio: Aliaksandr V. Krukau is an academic researcher from Rice University. The author has contributed to research in topics: Hybrid functional & Orbital-free density functional theory. The author has an hindex of 5, co-authored 6 publications receiving 4575 citations.

Influence of the exchange screening parameter on the performance of screened hybrid functionals.

Abstract: This work reexamines the effect of the exchange screening parameter ω on the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. We show that variation of the screening parameter influences solid band gaps the most. Other properties such as molecular thermochemistry or lattice constants of solids change little with ω. We recommend a new version of HSE with the screening parameter ω=0.11bohr−1 for further use. Compared to the original implementation, the new parametrization yields better thermochemical results and preserves the good accuracy for band gaps and lattice constants in solids.

Importance of short-range versus long-range Hartree-Fock exchange for the performance of hybrid density functionals

Abstract: We consider a general class of hybrid density functionals with decomposition of the exchange component into short-range and long-range parts. The admixture of Hartree-Fock (HF) exchange is controlled by three parameters: short-range mixing, long-range mixing, and range separation. We study how the variation of these parameters affects the accuracy of hybrid functionals for thermochemistry and kinetics. For the density functional component of the hybrids, we test three nonempirical approximations: local spin-density approximation, generalized gradient approximation (GGA), and meta-GGA. We find a great degree of flexibility in choosing the mixing parameters in range-separated hybrids. For the studied properties, short-range and long-range HF exchange seem to have a similar effect on the errors. One may choose to treat the long-range portion of the exchange by HF to recover the correct asymptotic behavior of the exchange potential and improve the description of density tail regions. If this asymptote is not important, as in solids, one may use screened hybrids, where long-range HF exchange is excluded. Screened hybrids retain most of the benefits of global hybrids but significantly reduce the computational cost in extended systems.

Hybrid functionals with local range separation.

Abstract: Range-separated (screened) hybrid functionals provide a powerful strategy for incorporating nonlocal exact (Hartree–Fock-type) exchange into density functional theory. Existing implementations of range separation use a fixed system-independent screening parameter. Here, we propose a novel method that uses a position-dependent screening function. These locally range-separated hybrids add substantial flexibility for describing diverse electronic structures and satisfy a high-density scaling constraint better than the fixed screening approximation does.

Self-consistent generalized Kohn-Sham local hybrid functionals of screened exchange: Combining local and range-separated hybridization

Abstract: We present local hybrid functionals that incorporate a position-dependent admixture of short-range (screened) nonlocal exact [Hartree-Fock-type (HF)] exchange. We test two limiting cases: screened local hybrids with no long-range HF exchange and long-range-corrected local hybrids with 100% long-range HF exchange. Long-range-corrected local hybrids provide the exact asymptotic exchange-correlation potential in finite systems, while screened local hybrids avoid the problems inherent to long-range HF exchange in metals and small-bandgap systems. We treat these functionals self-consistently using the nonlocal exchange potential constructed from Kohn-Sham orbital derivatives. Generalized Kohn-Sham calculations with screened and long-range-corrected local hybrids can provide accurate molecular thermochemistry and kinetics, comparable to existing local hybrids of full-range exchange. Generalized Kohn-Sham calculations with existing full-range local hybrids provide results consistent with previous non-self-consistent and “localized local hybrid” calculations. These new functionals appear to provide a promising extension of existing local and range-separated hybrids.

QM:QM embedding using electronic densities within an ONIOM framework: energies and analytic gradients.

Abstract: Accurate calculations of large systems remain a challenge in electronic structure theory. Hybrid energy techniques are a promising family of methods for treating such systems. Expanding on previous developments, we present a QM:QM electronic embedding model whereby the high-level region is polarized by the electron density of the low-level region within an ONIOM framework. A direct Coulomb embedding model as well a more computationally efficient model involving a density fitting expansion are considered. We also develop a generalized theory for the first derivatives of these classes of QM:QM electronic embedding schemes, which requires solution of a single set of self-consistent field response equations. Two initial test cases are presented and discussed.

Long-range corrected hybrid density functionals with damped atom–atom dispersion corrections

Abstract: We report re-optimization of a recently proposed long-range corrected (LC) hybrid density functional [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2008, 128, 084106] to include empirical atom–atom dispersion corrections. The resulting functional, ωB97X-D yields satisfactory accuracy for thermochemistry, kinetics, and non-covalent interactions. Tests show that for non-covalent systems, ωB97X-D shows slight improvement over other empirical dispersion-corrected density functionals, while for covalent systems and kinetics it performs noticeably better. Relative to our previous functionals, such as ωB97X, the new functional is significantly superior for non-bonded interactions, and very similar in performance for bonded interactions.

Black phosphorus field-effect transistors

Abstract: Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

Long-Range Corrected Hybrid Density Functionals with Damped Atom-Atom Dispersion Corrections

Abstract: Long-Range Corrected Hybrid Density Functionals with Damped Atom-Atom Dispersion Corrections Jeng-Da Chai ∗ and Martin Head-Gordon † Department of Chemistry, University of California and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA (Dated: June 14, 2008) We report re-optimization of a recently proposed long-range corrected (LC) hybrid density func- tionals [J.-D. Chai and M. Head-Gordon, J. Chem. Phys. 128, 084106 (2008)] to include empirical atom-atom dispersion corrections. The resulting functional, ωB97X-D yields satisfactory accuracy for thermochemistry, kinetics, and non-covalent interactions. Tests show that for non-covalent sys- tems, ωB97X-D shows slight improvement over other empirical dispersion-corrected density func- tionals, while for covalent systems and kinetics, it performs noticeably better. Relative to our previous functionals, such as ωB97X, the new functional is significantly superior for non-bonded interactions, and very similar in performance for bonded interactions. I. INTRODUCTION Due to its favorable cost-to-performance ratio, Kohn- Sham density-functional theory (KS-DFT) [1, 2] has be- come the most popular electronic structure theory for large-scale ground-state systems [3–5]. Its extension for treating excited-state systems [6, 7], time-dependent den- sity functional theory (TDDFT), has also been developed to the stage where it is now very widely used. The essential ingredient of KS-DFT, the exchange- correlation energy functional E xc , remains unknown and needs to be approximated. Semi-local gradient-corrected density functionals, though successful in many applica- tions, lead to qualitative failures in some circumstances, where the accurate treatment of non-locality of exchange- correlation hole becomes crucial. These situations occur mostly in the asymptotic regions of molecular systems, such as spurious self-interaction effects upon dissociation [8, 9] and dramatic failures for long-range charge-transfer excitations [10–12]. Widely used hybrid density function- als, like B3LYP [13, 14], do not qualitatively resolve these problems. These self-interaction errors can be qualitatively re- solved using the long-range corrected (LC) hybrid density functionals [15, 16, 18], which employ 100% Hartree-Fock (HF) exchange for long-range electron-electron interac- tions. This is accomplished by a partition of unity, using erf(ωr)/r for long-range (treated by HF exchange) and erfc(ωr)/r for short-range (treated by an exchange func- tional), with the parameter ω controlling the partition- ing. Over the past five years, the LC hybrid scheme has been attracting increasing attention [15] since its compu- tational cost is comparable with standard hybrid func- tionals [13]. However, LC functionals have tended to be inferior to the best hybrids for properties such as ther- mochemistry. ∗ Electronic † Author address: jdchai@berkeley.edu to whom correspondence should be addressed. Electronic address: mhg@cchem.berkeley.edu Recently we have improved the overall accuracy at- tainable with the LC functionals by using a systematic optimization procedure [18]. One important conclusion is that optimizing LC and hybrid functionals with identical numbers of parameters in their GGA exchange and cor- relation terms leads to noticeably better results for all properties using the LC form. The resulting LC func- tional is called ωB97. Further statistically significant improvement results from re-optimizing the entire func- tional with one extra parameter corresponding to an ad- justable fraction of short-range exact exchange, defining the ωB97X functional. Independent test sets covering thermochemistry and non-covalent interactions support these conclusions. However, problems associated with the lack of non-locality of the correlation hole, such as the lack of dispersion interactions (London forces), still remain, as the semi-local correlation functionals cannot capture long-range correlation effects [19, 20]. There have been significant efforts to develop a frame- work that can account for long-range dispersion effects within DFT. Zaremba and Kohn (ZK) [21] derived an exact expression for the second-order dispersion energy in terms of the exact density-density response functions of the two separate systems. To obtain a tractable non- local dispersion functional, Dobson and Dinite (DD) [22] made local density approximations to the ZK response functions. DD’s non-local correlation functional was ob- tained independently [23] by modifying the effective den- sity defined in the earlier work of Rapcewicz and Ashcroft Starting from the formally exact expression of KS- DFT, the adiabatic connection fluctuation-dissipation theorem (ACFDT), for the ground-state exchange- correlation energy, Langreth and co-workers [25] devel- oped a so-called van der Waals density functional (vdW- DF) by making a series of reasonable approximations to yield a computationally tractable scheme. Recently, Becke and Johnson (BJ) developed a series of post-HF correlation models with a novel treatment for dispersion interactions based on the exchange-hole dipole moment [26]. The origin of dispersion claimed in the BJ models was recently questioned by Alonso, and A.

Systematic optimization of long-range corrected hybrid density functionals.

Abstract: A general scheme for systematically modeling long-range corrected (LC) hybrid density functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochemistry, kinetics, and noncovalent interactions, when compared with common hybrid density functionals. The qualitative failures of the commonly used hybrid density functionals in some “difficult problems,” such as dissociation of symmetric radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid density functionals.

"Water-in-salt" electrolyte enables high-voltage aqueous lithium-ion chemistries.

Abstract: Lithium-ion batteries raise safety, environmental, and cost concerns, which mostly arise from their nonaqueous electrolytes. The use of aqueous alternatives is limited by their narrow electrochemical stability window (1.23 volts), which sets an intrinsic limit on the practical voltage and energy output. We report a highly concentrated aqueous electrolyte whose window was expanded to ~3.0 volts with the formation of an electrode-electrolyte interphase. A full lithium-ion battery of 2.3 volts using such an aqueous electrolyte was demonstrated to cycle up to 1000 times, with nearly 100% coulombic efficiency at both low (0.15 C) and high (4.5 C) discharge and charge rates.