Understanding DFT Calculations of Weak Interactions: Density-Corrected Density Functional Theory

Park, Hansol,Kim, Yeil,Sim, Eunji Korean Chemical Society 2019 대한화학회지 Vol.63 No.1

In this work, we discuss where the failure of Kohn-Sham Density Functional Theory (DFT) occurs in weak interactions. We have adopted density-corrected density functional calculations and dispersion correction separately to find out whether the failure is due to density-driven error or functional error. The results of Benzene Ar complex, one of the most common examples of van der Waals interactions, show that DFT calculations of van der Waals interaction suffer from functional error, rather than density-driven error. In addition, errors in DFT calculations of the S22 dataset, which contains small to relatively large (30 atoms) complexes with non-covalent interactions, are governed by functional errors.

Understanding DFT Calculations of Weak Interactions: Density-Corrected Density Functional Theory

박한솔,김예일,심은지 대한화학회 2019 대한화학회지 Vol.63 No.1

In this work, we discuss where the failure of Kohn-Sham Density Functional Theory (DFT) occurs in weak interactions. We have adopted density-corrected density functional calculations and dispersion correction separately to find out whether the failure is due to density-driven error or functional error. The results of Benzene·Ar complex, one of the most common examples of van der Waals interactions, show that DFT calculations of van der Waals interaction suffer from functional error, rather than density-driven error. In addition, errors in DFT calculations of the S22 dataset, which contains small to relatively large (30 atoms) complexes with non-covalent interactions, are governed by functional errors.

Recent advances in ensemble density functional theory and linear response theory for strong correlation

Lee Seunghoon,Park Woojin,Nakata Hiroya,Filatov Michael,Choi Cheol Ho 대한화학회 2022 Bulletin of the Korean Chemical Society Vol.43 No.1

The formulations and performances of spin-restricted ensemble-referenced KS and mixed-reference spin-flip time-dependent density functional theory incorporating strong correlations into density functional theories are documented. As a result of balanced dynamic and nondynamic correlation, they are capable of describing strongly correlated challenging systems including diradicals, bond dissociation, conical intersections, doubly excited states, and so on, overcoming the limitations of current density functional theories.

Constrained density functional theory calculations for estimation of forward and backward intermolecular charge transfer energy

김준석,김형준 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.8

Charge transfer (CT) in donor–acceptor complexes can occur in two directions: from donor to acceptor (forward CT, CT F ) and from acceptor to donor (backward CT, CT B ). For an ethylene and tetrafluoroethylene model system, coupled cluster calculations predict that CT F is more stable than CT B . Meanwhile, density functional theory (DFT) and time‐dependent DFT (TDDFT) employing B3LYP functional show a different CT state order depending on the Hartree–Fock exchange (HFX) contribution. The impact of basis sets as a possible cause to induce such unreasonable CT state reverse along with the increase of HFX was investigated. The physical origin of CT state reversal is examined in terms of molecular orbital energy. We analyzed two additional molecular pairs that feature CT state reversal along with the amount of HFX in B3LYP functional. Despite the reduced gap, we suggest constrained DFT using M06‐HF functional as an effective approach to estimate two CT state energies on equal footing.

Electronic states at 4,4´-N,N´-dicarbazol-biphenyl (CBP)emetal (Mg, Ag, and Au) interfaces: A joint experimental and theoretical study

Bhatt Mahesh Datt,Akahasi Baba,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.3

We used ultraviolet photoelectron spectroscopy (UPS) to study the electronic structure at the interface between organic semiconductor (CBP) and metals (Mg, Ag, and Au). Controlling the injection of charges at the interface requires a better understanding of the basic mechanism of the formation of interface states. In this context, photoelectron spectroscopy and density functional theory calculations were used to investigate the interaction of CBP with metal (111) surfaces. The position of HOMO relative to the Fermi level and the magnitude of the interface dipole were measured for each interface by UPS measurement. For CBP on Au, interface state (continuous state) was observed near the Fermi level by density functional theory calculations. However, no interface state was observed for CBP on Mg and Ag. It is suggested that the interface state plays an important role in charge transport at the interface. It was analyzed by density functional theory calculations that the interface state is formed due to interaction of CBP with metals and the position of the Fermi level varies strongly with the metal work function. The mechanism of formation of interface states and electrical properties were discussed.

Benchmarking study on time-dependent density functional theory calculations of electronic circular dichroism for gas-phase molecules

Jang, Heeseon,Kim, Nam Joon,Heo, Jiyoung Elsevier 2018 Computational & theoretical chemistry Vol.1125 No.-

<P><B>Abstract</B></P> <P>Time-dependent density functional (TDDFT) theory has become a popular method to calculate electronic excited states. The electronic circular dichroism (ECD) spectra of chiral molecules can be computed by TDDFT to resolve their absolute configurations. In this work, we evaluated the performance of TDDFT to calculate ECD of three chiral molecules whose vibronic CD spectra in a supersonic jet were recently reported. We tested seven different functionals (PBEPBE, PBE1PBE, B3LYP, mPW1PW91, M06-2X, CAM-B3LYP, and ωB97X-D) with different levels of the Pople basis set to predict the rotatory strengths of both vertical and adiabatic excitations of the chiral molecules. The 6-311++G(d,p) basis set is appropriate for the ECD calculation, and the augmentation of the diffuse function improves the quality of basis set in calculating the rotatory strength. The simulations of vibronic CD spectra under the adiabatic Hessian scheme in Cartesian coordinates have been feasible only with the M06-2X, CAM-B3LYP, and ωB97X-D functionals. The rotatory strength signs for the 0–0 transition of (1<I>R</I>, 2<I>S</I>)-ephedrine and (<I>S</I>)-2-amino-1-phenylethanol agree well with the experimental results. For the (1<I>S</I>, 2<I>S</I>)-pseudoephedrine conformers, the rotatory strength signs predicted using those three functionals are consistent with each other but do not coincide with the experimental results. The PBEPBE and B3LYP functionals are not robust for geometry optimizations in TDDFT because the calculations using these functionals do not provide reasonable equilibrium geometries for some conformers in the S<SUB>1</SUB> state. Comparison with the conformation-specific CD spectra provides the unambiguous assessment of the DFT functionals suitable for ECD calculations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The accuracy of TDDFT in computing conformation-specific ECD is estimated. </LI> <LI> The simulations of vibronic CD spectra are feasible only with the M06-2X, CAM-B3LYP, and ωB97X-D functionals. </LI> <LI> The PBEPBE and B3LYP functionals are not robust for geometry optimizations in TDDFT. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tuning the Photoluminescence of Graphene Quantum Dots through the Charge Transfer Effect of Functional Groups

Jin, Sung Hwan,Kim, Da Hye,Jun, Gwang Hoon,Hong, Soon Hyung,Jeon, Seokwoo American Chemical Society 2013 ACS NANO Vol.7 No.2

<P>The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1–3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (<I>ca</I>. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the amine-functionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-2/nn304675g/production/images/medium/nn-2012-04675g_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn304675g'>ACS Electronic Supporting Info</A></P>

Atomic and Electronic Structure of Au/Si(111)-(√3 × √3)R30˚: Density-Functional Theory Calculations

Ji Young Lee,강명호 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6

The atomic and electronic structure of the Au/Si(111)-(√3 × √3)R30˚ surface has been studied by density-functional theory calculations. We examined the potential energy surface for various Au adsorption configurations with 1 monolayer coverage and identified two local-energy minimum structures, which correspond to the twisted trimer (TT) model and the conjugate honeycombchained- trimer (CHCT) model. The honeycomb-chained-trimer (HCT) model, reported as a stable structure in a previous study, turned out to be locally unstable. The TT model is slightly more stable by 0.01 eV than the CHCT model, and there is an energy barrier of 0.05 eV between the two models. While the TT and CHCT models produce similar scanning-tunneling-microscopy simulation images, comparing well with experiments, their surface band structures are distinct in energy and dispersion, but both of them are in partial disagreement with angle-resolved photoelectron spectroscopy measurements. The atomic and electronic structure of the Au/Si(111)-(√3 × √3)R30˚ surface has been studied by density-functional theory calculations. We examined the potential energy surface for various Au adsorption configurations with 1 monolayer coverage and identified two local-energy minimum structures, which correspond to the twisted trimer (TT) model and the conjugate honeycombchained- trimer (CHCT) model. The honeycomb-chained-trimer (HCT) model, reported as a stable structure in a previous study, turned out to be locally unstable. The TT model is slightly more stable by 0.01 eV than the CHCT model, and there is an energy barrier of 0.05 eV between the two models. While the TT and CHCT models produce similar scanning-tunneling-microscopy simulation images, comparing well with experiments, their surface band structures are distinct in energy and dispersion, but both of them are in partial disagreement with angle-resolved photoelectron spectroscopy measurements.

범밀도함수론을 이용한 백금, 팔라듐, 니켈, 크롬과 수소반응성 연구

김태완,박태성,정연성,강영진,이택홍 한국수소및신에너지학회 2014 한국수소 및 신에너지학회논문집 Vol.25 No.3

To study catalytic activity and hydrogen embrittlement of Pd, Pt, Ni, and Cr in fuel cell electrode,we used density-functional theory. The calculation tools based electron density give much shorter calculation timeand cheap costs. Maximum of bond overlap populations of each metal are 0.6539eV for Pd-H, 0.6711eV for Pt-H,0.6323eV for Ni-H, 0.6152eV for Cr-H. Electron density of Cr has strongest in related metals, which shows stronglocalization of electron, implying anti hydrogen embrittlement behaviors.

Comparative studies of density functionals in modelling hydrogen bonding energetics of acrylamide dimers

Lin, Yi-De,Wang, Yi-Siang,Chao, Sheng D. Techno-Press 2017 Coupled systems mechanics Vol.6 No.3

Intermolecular interaction energies and conformer geometries of the hydrogen bonded acrylamide dimers have been studied by using the second-order Møller-Plesset (MP2) perturbation theory and the density functional theory (DFT) with 17 density functionals. Dunning's correlation consistent basis sets (up to aug-cc-pVTZ) have been used to study the basis set effects. The DFT calculated interaction energies are compared to the reference energy data calculated by the MP2 method and the coupled cluster method at the complete basis set (CCSD(T)/CBS) limit in order to determine the relative performance of the studied density functionals. Overall, dispersion-energy-corrected density functionals outperform uncorrected ones. The ${\omega}B97XD$ density functional is particularly effective in terms of both accuracy and computational cost in estimating the reference energy values using small basis sets and is highly recommended for similar calculations for larger systems.