Sang Soo Han

We report the H2 uptake properties of six covalent organic frameworks (COFs) from first-principles-based grand canonical Monte-Carlo simulations. The predicted H2 adsorption isotherm is in excellent agreement with the only available experimental result (3.3 vs 3.4 wt % at 50 bar and 77 K for COF-5), also reported here, validating the predictions. We predict that COF-105 and COF-108 lead to a reversible excess H2 uptake of 10.0 wt % at 77 K, making them the best known storage materials for molecu

This critical review covers the application of computer simulations, including quantum calculations (ab initio and DFT), grand canonical Monte-Carlo simulations, and molecular dynamics simulations, to the burgeoning area of the hydrogen storage by metal-organic frameworks and covalent-organic frameworks. This review begins with an overview of the theoretical methods obtained from previous studies. Then strategies for the improvement of hydrogen storage in the porous materials are discussed in de

To maximize reversible H2 storage near room temperature and modest pressures, we propose Li doping of the metal-organic framework (MOFs) structures developed by the Yaghi group at UCLA (constructed using octahedral Zn−O−C clusters with aromatic carbon ring linkers). We tested this design using grand canonical Monte Carlo simulations with first-principles derived force fields and predict that at −30 °C and 100 bar the Li−MOF-C30 leads gravimetric H2 uptake of 6.0 wt %, reaching the 2010 Departmen

Quick on the uptake: The metal–organic framework Mg-MOF-C30 (see picture) contains Mg4O(CO2)6 building units (pink) and aromatic organic linkers containing 30 carbon atoms (teal). This material leads to 8.08 wt % H2 uptake at 77 K and 20 bar, the highest among investigated MOF structures.

Using molecular dynamics (MD) simulations, we show that metal−organic frameworks (MOFs) constructed using octahedral Zn4O(CO2)6 clusters linked via aromatic carbon ring structures lead to negative thermal expansion (NTE) behavior (from 0 K to melting). We find that MOF-C22 contracts volumetrically by 1.9% over the range of 0 to 600 K, making it one of the best NTE materials (linear expansion coefficient of α = −11.05 × 10-6 K-1 compared with α = −9.1 × 10-6 K-1 found for ZrW2O8, previously the c

We introduce the reactive force field (ReaxFF) simulation to predict the hydrolysis reactions and water stability of metal-organic frameworks (MOFs) where the simulation showed that MOF-74 has superior water-resistance compared with isoreticular IRMOF-1 and IRMOF-10.

To make a practical molecular dynamics (MD) simulation of the large-scale reactive chemical systems of Li-H and Li-C, we have optimized parameters of the reactive force field (ReaxFF) for these systems. The parameters for this force field were obtained from fitting to the results of density functional theory (DFT) calculations on the structures and energy barriers for a number of Li-H and Li-C molecules, including Li(2), LiH, Li(2)H(2), H(3)C-Li, H(3)C-H(2)C-Li, H(2)C=C-LiH, HCCLi, H(6)C(5)-Li,

The development of catalysts for the electrochemical N2 reduction reaction (NRR) with a low limiting potential and high Faradaic efficiency is highly desirable but remains challenging. Here, to achieve acceleration, we develop and report a slab graph convolutional neural network (SGCNN), an accurate and flexible machine learning (ML) model that is suited for probing surface reactions in catalysis. With a self-accumulated database of 3040 surface calculations at the density-functional-theory (DFT

Using first-principles calculations, we describe and compare atomistic lithiation, sodiation, and magnesiation processes in black phosphorous with a layered structure similar to graphite for Li-, Na-, and Mg-ion batteries because graphite is not considered to be an electrode material for Na- and Mg-ion batteries. The three processes are similar in that an intercalation mechanism occurs at low Li/Na/Mg concentrations, and then further insertion of Li/Na/Mg leads to a change from the intercalation

Stimulated by the recent report by Yaghi and co-workers of hexagonal metal−organic frameworks (MOF) exhibiting reversible binding of up to 7.5 wt % at 77 K and 70 bar for MOF-177 (called here IRMOF-2-24), we have predicted additional trigonal organic linkers, including IRMOF-2-60, which we calculate to bind 9.7 wt % H2 storage at 77 K and 70 bar, the highest known value for 77 K. These calculations are based on grand canonical Monte Carlo (GCMC) simulations using force fields that match accurate

We present a new reactive force field ReaxFF(HBN) derived to accurately model large molecular and condensed phase systems of H, B, and N atoms. ReaxFF(HBN) has been tested against quantum calculation data for B-H, B-B, and B-N bond dissociations and for H-B-H, B-N-B, and N-B-N bond angle strain energies of various molecular clusters. The accuracy of the developed ReaxFF(HBN) for B-N-H systems is also tested for (i) H-B and H-B bond energies as a function of out of plane in H-B(NH2)3 and H-N(BH2)

Using density functional theory (DFT) calculations, we have studied structural models of graphite fluorides for five fluorine compositions; C1F (CF1), C2F (CF0.5), C3F (CF0.33), C4F (CF0.25), and C16F (CF0.0625). For each composition, we considered several possible structural models and calculated heat of formation relative to the pristine graphite and F2 molecule. We also simulated X-ray diffraction patterns for each structural model and compared those with experiments. We find, in agreement wi

We report the H2 uptake behavior of 10 zeolitic−imidazolate frameworks (ZIFs), based on grand canonical Monte Carlo (GCMC) simulations. The force fields (FFs) describing the interactions between H2 and ZIF in the GCMC were based on ab initio quantum mechanical (QM) calculations (MP2) aimed at correctly describing London dispersion (van der Waals attraction). Thus these predictions of H2 uptake are based on first principles (non empirical) and hence applicable to new framework materials for which

The electrochemical nitrogen reduction reaction (NRR) has been regarded as a promising alternative to the conventional Haber–Bosh process for NH3 synthesis. Inspired by the Fe–Mo–S cofactor in the enzyme nitrogenase, metal sulfide catalysts, mostly Fe- or Mo-based sulfides, have recently received great interest. Here, we propose Cu2–xS (0 ≤ x < 1) as an efficient NRR electrocatalyst. Electrochemical tests at room temperature and atmospheric pressure reveal that Cu1.81S achieves a high NH3 yield