Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- Water clusters (4)
- Computational chemistry (3)
- Thermodynamics (3)
- Ab initio electronic structure theory (2)
- Anharmonicity (2)
-
- Enthalpy (2)
- Entropy (2)
- Free energies (2)
- Frequency scaling factors (2)
- Harmonic approximation (2)
- Harmonic frequencies (2)
- Simple perturbation theory (2)
- Thermal corrections (2)
- Zero-point vibrational energy (2)
- Aerosol formation (1)
- Anharmonic (1)
- CBS (1)
- CCSD(T) (1)
- Complete basis set limit (1)
- Electron correlation (1)
- Hydration (1)
- Hydronium (1)
- MP2 (1)
- Quantum chemistry (1)
- RI-MP2 (1)
- Rotational spectroscopy (1)
- Sulfuric acid hydration (1)
- Water dimer (1)
- File Type
Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Benchmark Structures And Binding Energies Of Small Water Clusters With Anharmonicity Corrections, Berhane Temelso, Kaye A. Archer, George C. Shields
Benchmark Structures And Binding Energies Of Small Water Clusters With Anharmonicity Corrections, Berhane Temelso, Kaye A. Archer, George C. Shields
Berhane Temelso
For (H2O)n where n = 1–10, we used a scheme combining molecular dynamics sampling with high level ab initio calculations to locate the global and many low lying local minima for each cluster. For each isomer, we extrapolated the RI-MP2 energies to their complete basis set limit, included a CCSD(T) correction using a smaller basis set and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled and unscaled harmonic vibrational frequencies. The vibrational scaling factors were determined specifically for water clusters by comparing harmonic frequencies with VPT2 fundamental frequencies. We find the CCSD(T) correction to the RI-MP2 binding …
Structural Analysis Of Alpha-Fetoprotein (Afp)-Like Peptides With Anti-Breast-Cancer Properties, Berhane Temelso, Katherine Alser, Arianne Gauthier, Amber Palmer, George Shields
Structural Analysis Of Alpha-Fetoprotein (Afp)-Like Peptides With Anti-Breast-Cancer Properties, Berhane Temelso, Katherine Alser, Arianne Gauthier, Amber Palmer, George Shields
Berhane Temelso
The abundance of alpha-fetoprotein (AFP), a natural protein produced by the fetal yolk sac during pregnancy, correlates with lower incidence of estrogen receptor positive (ER+) breast cancer. The pharmacophore region of AFP has been narrowed down to a four amino acid (AA) region in the third domain of the 591 AA peptide. Our computational study focuses on a 4-mer segment consisting of the amino acids threonine-proline-valine-asparagine (TPVN). We have run replica exchange molecular dynamics (REMD) simulations and used 120 configurational snapshots from the total trajectory as starting configurations for quantum chemical calculations. We optimized structures using semiempirical (PM3, PM6, PM6-D2, …
Hydration Of The Bisulfate Ion: Atmospheric Implications, Devon Husar, Berhane Temelso, Alexa Ashworth, George Shields
Hydration Of The Bisulfate Ion: Atmospheric Implications, Devon Husar, Berhane Temelso, Alexa Ashworth, George Shields
Berhane Temelso
Using molecular dynamics configurational sampling combined with ab initio energy calculations, we determined the low energy isomers of the bisulfate hydrates. We calculated the CCSD(T) complete basis set (CBS) binding electronic and Gibbs free energies for 53 low energy isomers of HSO4–(H2O)n=1–6 and derived the thermodynamics of adding waters sequentially to the bisulfate ion and its hydrates. Comparing the HSO4–/H2O system to the neutral H2SO4/H2O cluster, water binds more strongly to the anion than it does to the neutral molecules. The difference in the binding thermodynamics of HSO4–/H2O and H2SO4/H2O systems decreases with increasing number of waters. The thermodynamics for …
Structures Of Cage, Prism, And Book Isomers Of Water Hexamer From Broadband Rotational Spectroscopy, Cristóbal Pérez, Matt Muckle, Daniel Zaleski, Nathan Seifert, Berhane Temelso, George Shields, Zbigniew Kisiel, Brooks Pate
Structures Of Cage, Prism, And Book Isomers Of Water Hexamer From Broadband Rotational Spectroscopy, Cristóbal Pérez, Matt Muckle, Daniel Zaleski, Nathan Seifert, Berhane Temelso, George Shields, Zbigniew Kisiel, Brooks Pate
Berhane Temelso
Theory predicts the water hexamer to be the smallest water cluster with a three-dimensional hydrogen-bonding network as its minimum energy structure. There are several possible low-energy isomers, and calculations with different methods and basis sets assign them different relative stabilities. Previous experimental work has provided evidence for the cage, book, and cyclic isomers, but no experiment has identified multiple coexisting structures. Here, we report that broadband rotational spectroscopy in a pulsed supersonic expansion unambiguously identifies all three isomers; we determined their oxygen framework structures by means of oxygen-18–substituted water (H218O). Relative isomer populations at different expansion conditions establish that the …
Structure And Thermodynamics Of H3o+(H2o)8 Clusters: A Combined Molecular Dynamics And Quantum Mechanics Approach, Berhane Temelso, Thorsten Koddermann, Karl K. Kirschner, Katurah L. Klein, George C. Shields
Structure And Thermodynamics Of H3o+(H2o)8 Clusters: A Combined Molecular Dynamics And Quantum Mechanics Approach, Berhane Temelso, Thorsten Koddermann, Karl K. Kirschner, Katurah L. Klein, George C. Shields
Berhane Temelso
We have studied the structure and stability of (H3O+)(H2O)8 clusters using a combination of molecular dynamics sampling and high-level ab initio calculations. 20 distinct oxygen frameworks are found within 2 kcal/mol of the electronic or standard Gibbs free energy minimum. The impact of quantum zero-point vibrational corrections on the relative stability of these isomers is quite significant. The box-like isomers are favored in terms of electronic energy, but with the inclusion of zero-point vibrational corrections and entropic effects tree-like isomers are favored at higher temperatures. Under conditions from 0 to 298.15 K, the global minimum is predicted to be a …
Quantum Mechanical Study Of Sulfuric Acid Hydration: Atmospheric Implications, Berhane Temelso, Thomas Morrell, Robert Shields, Marco Allodi, Elena Wood, Karl Kirschner, Thomas Castonguay, Kaye Archer, George Shields
Quantum Mechanical Study Of Sulfuric Acid Hydration: Atmospheric Implications, Berhane Temelso, Thomas Morrell, Robert Shields, Marco Allodi, Elena Wood, Karl Kirschner, Thomas Castonguay, Kaye Archer, George Shields
Berhane Temelso
The role of the binary nucleation of sulfuric acid in aerosol formation and its implications for global warming is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the thermodynamics of sulfuric acid hydration using ab initio quantum mechanical methods. For H2SO4(H2O)n where n = 1–6, we used a scheme combining molecular dynamics configurational sampling with high-level ab initio calculations to locate the global and many low lying local minima for each cluster size. For each isomer, we extrapolated the Møller–Plesset perturbation theory (MP2) energies to their complete basis set (CBS) limit and added finite temperature corrections …
Computational Study Of The Hydration Of Sulfuric Acid Dimers: Implications For Acid Dissociation And Aerosol Formation, Berhane Temelso, Thuong Ngoc Phan, George C. Shields
Computational Study Of The Hydration Of Sulfuric Acid Dimers: Implications For Acid Dissociation And Aerosol Formation, Berhane Temelso, Thuong Ngoc Phan, George C. Shields
Berhane Temelso
We have investigated the thermodynamics of sulfuric acid dimer hydration using ab initio quantum mechanical methods. For (H2SO4)2(H2O)n where n = 0−6, we employed high-level ab initio calculations to locate the most stable minima for each cluster size. The results presented herein yield a detailed understanding of the first deprotonation of sulfuric acid as a function of temperature for a system consisting of two sulfuric acid molecules and up to six waters. At 0 K, a cluster of two sulfuric acid molecules and one water remains undissociated. Addition of a second water begins the deprotonation of the first sulfuric acid …
The Role Of Anharmonicity In Hydrogen-Bonded Systems: The Case Of Water Clusters, Berhane Temelso, George Shields
The Role Of Anharmonicity In Hydrogen-Bonded Systems: The Case Of Water Clusters, Berhane Temelso, George Shields
Berhane Temelso
The nature of vibrational anharmonicity has been examined for the case of small water clusters using second-order vibrational perturbation theory (VPT2) applied on second-order Møller–Plesset perturbation theory (MP2) potential energy surfaces. Using a training set of 16 water clusters (H2O)n=2–6,8,9 with a total of 723 vibrational modes, we determined scaling factors that map the harmonic frequencies onto anharmonic ones. The intermolecular modes were found to be substantially more anharmonic than intramolecular bending and stretching modes. Due to the varying levels of anharmonicity of the intermolecular and intramolecular modes, different frequency scaling factors for each region were necessary to achieve the …
Broadband Fourier Transform Rotational Spectroscopy For Structure Determination: The Water Heptamer, Cristóbal Pérez, Simon Lobsiger, Nathan A. Seifert, Daniel P. Zaleski, Berhane Temelso, George C. Shields, Zbigniew Kisiel, Brooks H. Pate
Broadband Fourier Transform Rotational Spectroscopy For Structure Determination: The Water Heptamer, Cristóbal Pérez, Simon Lobsiger, Nathan A. Seifert, Daniel P. Zaleski, Berhane Temelso, George C. Shields, Zbigniew Kisiel, Brooks H. Pate
Berhane Temelso
Over the recent years chirped-pulse, Fourier-transform microwave (CP-FTMW) spectrometers have chan- ged the scope of rotational spectroscopy. The broad frequency and large dynamic range make possible structural determinations in molecular systems of increasingly larger size from measurements of heavy atom (13C, 15N, 18O) isotopes recorded in natural abundance in the same spectrum as that of the parent isotopic species. The design of a broadband spectrometer operating in the 2–8 GHz frequency range with further improvements in sensitivity is presented. The current CP-FTMW spectrometer performance is benchmarked in the analyses of the rotational spectrum of the water …