Bala Ramachandran - Academia.edu (original) (raw)
Papers by Bala Ramachandran
Proceedings - Frontiers in Education Conference, FIE, 2008
Louisiana Tech University's College of Engineering and Science has over ten years experience oper... more Louisiana Tech University's College of Engineering and Science has over ten years experience operating under an innovative multidisciplinary administrative structure which has created a supportive environment for numerous education reform initiatives. The traditional departmental structure was dismantled in favor of a much more flexible approach which has helped remove barriers between departments and promoted collaboration between engineering and science programs. The new administrative structure relies heavily on multidisciplinary teams and has been a key factor in the successful establishment of our first Integrated Engineering Curriculum in 1997, followed by our Integrated Science Curriculum in 2002. Other innovations implemented since that time include the first undergraduate nanosystems engineering degree program in the US; multidisciplinary design courses which include engineering, business, and technical writing students; a freshman enrichment program; the Living with the Lab curriculum (the most recent version of our Integrated Engineering Curriculum); and a program whereby engineering and science majors complete the Master of Arts in Teaching and become certified K-12 teachers. The College currently has $3.5 million in NSF funding for STEM projects. Much of the lasting success of these education reform efforts can be attributed to the supportive, interdisciplinary approaches the College uses in all of its core functions, including undergraduate education, research, and graduate education.
The Journal of Physical Chemistry C, 2012
Carbon chemisorption on iron nanoparticles at small carbon coverage has been studied by using a F... more Carbon chemisorption on iron nanoparticles at small carbon coverage has been studied by using a Fe 13 particle as a model because it possesses a nearly icosahedral geometry, and complications with additional effects associated with the surface inhomogeneity do not arise. The electronic and geometrical structures of Fe 13 C n are computed for n = 0−20 using an all-electron density functional theory with generalized gradient approximation and a rather large basis set. It is found that the energetically preferred structures correspond to the formation of carbon dimers up to Fe 13 C 12 and trimers up to Fe 13 C 18 in octahedral configurations of the dimers and trimers with the Fe 13 cluster being endohedral. The trend for the formation of carbon tetramers breaks at Fe 13 C 20. We found that the dependence of the total energy on the total spin is nearly the same for Fe 13 and Fe 13 C 8. When the number of chemisorbed carbon atoms exceeds 6, chemisorption quenches the total magnetic moment to 36 μ B from the value of 44 μ B in the ground-state Fe 13 cluster. We used natural atomic orbital populations to understand why the quenching does not depend on the number of chemisorbed atoms. Free C n species were reoptimized at the same level of theory to calculate the dissociation energies of C n and Fe 13 C n. It is found that the largest fragmentation energy of 12 eV belongs to the Fe 13 C 12 → Fe 13 + C 12 channel. Finally, we found that atomization energies for the carbon chemisorbed on the iron particle are larger by approximately 10 eV than atomization energies of the corresponding free carbon particles, which can be related to the catalytic strength of the Fe 13 particle. 49 total number reached 20, which is the number of triangular faces 50 in the Fe 13 icosahedral cluster. These faces are expected to be the 51 preferred bonding sites according to the electron localization 52 function (ELF) study 18 performed for Fe 4. Indeed, our computa-53 tional studies have shown that the face attachment of O or N to 54 Fe 4 and Fe 6 clusters 19,20 as well as C to a Fe 4 cluster 21 is preferred 55 when the number of carbon atoms is small. 56 Our computations on Fe 13 C n clusters (n = 1−20) are 57 performed using an all-electron DFT method with generalized 58 gradient approximation and a rather large basis set. We optimized 59 also the ground-state C n species (n = 2−20) at the same level of 60 theory so that the energetics of the carbon−carbon binding in the 61 gas phase could be compared to that in the presence of an Fe 13 62 particle. To gain insight into the carbon chemisorption 63 dependence on the spin multiplicity, we performed optimizations 64 of Fe 13 and Fe 13 C 8 in the whole range of the spin multiplicities 65 from 1 to 47. 66 Small precursors of these carbon allotropes were the subject 67 of numerous experimental and theoretical investigations. Smalley
The Journal of Chemical Physics, 2013
The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn... more The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni13, Cu13, Zn12, and Zn13 are found to be different from the geometries of the corresponding neutral parents. The computed ionization energies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M13 and M13+ clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 μB. Exceptions are found only fo...
American Journal of Infection Control, 2006
Background: Routine surveillance of nosocomial infections has become an integral part of infectio... more Background: Routine surveillance of nosocomial infections has become an integral part of infection control and quality assurance in US hospitals. Methods: As part of the International Nosocomial Infection Control Consortium, we performed a prospective nosocomial infection surveillance cohort study in 5 adult intensive care units of 4 Mexican public hospitals using the Centers for Disease Control and Prevention National Nosocomial Infections Surveillance system definitions. Site-specific nosocomial infection rates were calculated. Results: The overall nosocomial infection rate was 24.4% (257/1055) and 39.0 (257/6590) per 1000 patient days. The most common infection was catheter-associated bloodstream infection, 57.98% (149/257), followed by ventilator-associated pneumonia, 20.23% (52/257), and catheter-associated urinary tract infection, 21.79% (56/257). The overall rate of catheter-associated bloodstream infections was 23.1 per 1000 device-days (149/6450); ventilator-associated pneumonia rate was 21.8 per 1000 device-days (52/2390); and catheter-associated urinary tract infection rate was 13.4 per 1000 device-days (56/4184). Conclusion: Our rates are similar to other hospitals of Latin America and higher than US hospitals.
The Journal of Physical Chemistry A, 2003
Bond dissociation energies for the hypofluorous acid (HOF) system and an anharmonic force field f... more Bond dissociation energies for the hypofluorous acid (HOF) system and an anharmonic force field for HOF are obtained from ab initio energies at the CCSD(T)/CBS level of theory, where the complete basis set (CBS) limit energies are obtained by extrapolating CCSD(T)/aug-cc-pVnZ (n) 2, 3, and 4) energies. The effects of including core-valence correlation and scalar relativistic effects on the thermochemical and spectroscopic properties are investigated. The results are compared to available experimental results including recent reevaluations of the properties of OF and OH. Quartic force fields are calculated at each level of theory and basis set used. Excellent agreement between experimental and calculated properties is obtained in most cases, but a few prominent and large differences in rotation-vibration coupling constants and a few force constants are observed. In these cases, our results are consistent with other, high-level, ab initio evaluations of these properties. Given the ability of large basis set CCSD(T) calculations to yield accurate results for a wide range of molecular parameters, these differences suggest that experimental results may benefit from reexamination in some cases. A new recommendation for the 0 K enthalpy of formation of HOF, ∆H°f ,0K)-20.02 (0.25 kcal/mol, is presented based on a careful analysis of recent experimental data and is supported by the high-level ab initio calculations presented in this work.
The Journal of Organic Chemistry, 2007
The influence of temperature and solvent effects on the reduction and amination mechanisms of iod... more The influence of temperature and solvent effects on the reduction and amination mechanisms of iodomethane by lithium N,N-diisopropylaminoborohydride (iPr-LAB) was examined in varying concentrations of THF and dioxane. The reactions of benzyl chloride and trimethylsilyl chloride with iPr-LAB in THF were also studied. The amination of iodomethane is favored over reduction at low and room temperatures in pure THF and with increasing the amount of dioxane in THF. At higher temperatures, the reduction reaction appears to compete with the amination. In dioxane solvent, however, iodomethane yields exclusively the amination product regardless of temperature. On the other hand, reduction by iPr-LAB to the aminoborane is the only product observed in THF when benzyl chloride and trimethylsilyl chloride are used. To understand the solvent effects on the product distribution, ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane and bromomethane by lithium dimethylaminoborohydride (LAB) in THF and dioxane. The results of these calculations show that the relative reaction barrier heights are significantly affected by the nature of the coordinated solvent molecule and thus lend support to the experimental observations.
The Journal of Organic Chemistry, 2005
Journal of Chemical Education, 1994
Drooram disks 3 5 n or 5 25 in ; 1 free a & contamng sir.ctu& from Broo<naven hatonal Laooralory ... more Drooram disks 3 5 n or 5 25 in ; 1 free a & contamng sir.ctu& from Broo<naven hatonal Laooralory Prole n Data Ban6 Man-al 303 pp F gs ana Cnans, OJCA Reference 36 pp ] The meat advances in the Dower of micro~raeessors has made it quite practical to use relatively inexpensive personal computers for demonstrating, teaching, and exploring the principles of molecular structure and banding. Considering the pedagogic value of constructing, optimizing, and manipulating the structure of a molecule an a computer, it is tempting to say that such exercises must be an integral part of any advanced undergraduate or graduate course dealing with these topics. The MOBYMolecular Modelling on the PC version 1.5 is intended for just this type of classroom or self-study activity MOBY, uf cuurse, permits rhe cdorful display .f molccules, sl,owtng the m m s n i pmnts, crrcles,or thc~rorns nnd hnndsm the .'ball-and.irwk' rrprtirntstion. Apart from thlri, the pn,L?um boasts a long and impressive list of features, and among them are geometry optimization based an force-field calculations, conformational analysis, molecular dynamics simulations, and semi-empirical quantum chemistry calculations based an the MNDO (1) and AM1 (2) algorithms. The user is given three modes of operation. The "normal" mode provides the full features of the package, and is the default. A "protocol" mode permits the recording of a demonstration or teaching session, which the third mode, "demo", plays back. The documentation consists of a 303-page manual with a good index and a Quick Reference guide. The installation was easy and involved no surprises. The program came with a free disk containing a few protein structures from the Protein Data Bank of Brookhaven National Laboratory. The protein structures were supplied in a sin& executable file BRKHVN.EXE. from which the actual .. srruernrc.; h a w r u be cxll-ncrrd by running the wrnmand BRKIfl'N H o w w w , thwr IS nn mentmn of thls fact trt the docurnrnratwn ur in toe "HEAlJ ME" file thdr suppuscdly contains w-Volume 71 Number
Natural Computing Series
Cluster geometry optimization is an important problem from the Chemistry area. Hybrid approaches ... more Cluster geometry optimization is an important problem from the Chemistry area. Hybrid approaches combining evolutionary algorithms and gradientdriven local search methods are one of the most efficient techniques to perform a meaningful exploration of the solution space to ensure the discovery of low energy geometries. Here we perform a comprehensive study on the locality properties of this approach to gain insight on the algorithm's strengths and weaknesses. The analysis is accomplished through the application of several static measures to randomly generated solutions in order to establish the main properties of an extended set of mutation and crossover operators. Locality analysis is complemented with additional results obtained from optimization runs. The combination of the outcomes allows us to propose a robust hybrid algorithm that is able to quickly discover the arrangement of the cluster's particles that correspond to optimal or near-optimal solutions.
Chemical Physics Letters, 2000
The Journal of Organic Chemistry, 2005
Gas-phase activation energies were calculated for three lithium enolate reactions by using severa... more Gas-phase activation energies were calculated for three lithium enolate reactions by using several different ab initio and density functional theory (DFT) methods to determine which levels of theory generate acceptable results. The reactions included an aldol-type addition of an enolate to an aldehyde, a proton transfer from an alcohol to a lithium enolate, and an S N 2 reaction of an enolate with chloromethane. For each reaction, the calculations were performed for both the monomeric and dimeric forms of the lithium enolate. It was found that transition state geometry optimization with B3LYP followed by single point MP2 calculations generally provided acceptable results compared to higher level ab initio methods.
![Research paper thumbnail of Dynamics of the O([sup 3]P)+HCl reaction on the [sup 3]A[sup ʺ] electronic state: A new ab initio potential energy surface, quasi-classical trajectory study, and comparison to experiment](https://attachments.academia-assets.com/81200666/thumbnails/1.jpg)
](The Journal of Chemical Physics, 1999
A new potential energy surface for the lowest electronic state of the O() + HCl system is present... more A new potential energy surface for the lowest electronic state of the O() + HCl system is presented. This surface is based on electronic energies calculated at the multireference configuration interaction level of theory with the Davidson correction (MR-CI+Q) using the Dunning cc-pVTZ one-electron basis sets. The ab initio energies thus obtained are scaled using the Scaled External Correlation (SEC) method of Brown and Truhlar. The SEC-scaled energies are fitted to a simple analytical expression to yield a potential energy surface which correlates the reactants O() + HCl() to the products OH() + Cl(). The reaction barrier on this surface lies at an O-H-Cl angle of 131.4 at an energy of 9.78 kcal/mol above the asymptotic O + HCl minimum. This barrier is 1.3 kcal/mol higher than that on the potential energy surface obtained by Koizumi, Schatz, and Gordon (KSG) [J. Chem. Phys. 95, 6421 (1991)] and 1.1 kcal/mol lower than the S2 surface of Ramachandran, Senekowitsch, and Wyatt (RSW) [J. Mol. Struct. (Theochem) 454, 307 (1998)]. The dynamics of the reaction O() + HCl () OH() + Cl on this potential surface is studied using quasi-classical trajectory (QCT) propagation and the results are compared to the experimental observations of
Lower bounds for the quadratic assignment problem (QAP) tend to deteriorate rapidly with the size... more Lower bounds for the quadratic assignment problem (QAP) tend to deteriorate rapidly with the size of the QAP. Recently, Resende, Ramakrishnan, and Drezner (1995) computed a linear programming based lower bound for the QAP using an interior point algorithm for linear programming to solve the linear programming relaxation of a classical integer programming forn~ulation of the QAP. That linear progralil can be viewed as a two-body interaction formulation. Those bounds were found to be the tightest for a large number of instances from QAPLIB, a library of QAP test problems. In this paper, we apply the same interior point approach to compute lower bounds derived from the three-body interaction formulation of Ramachandran and Pekny (1996). All instances from QAPLIB, having dimension up to n = 12, were solved. The new approach produces tight lower hounds (lower bounds equal to the optimal solution) for all instances tested. Attempts to solve the linear programming relaxations with CPLEX (primal simplex, dual simplex, and barrier interior point method) were successful only for the smallest instances (n 5 6 for the barrier method, n 5 7 for tlle primal simplex method, and n 5 8 for the dual simplex method).
In spite of many advances in business process modeling and simulation technologies, their adoptio... more In spite of many advances in business process modeling and simulation technologies, their adoption by the business analyst community has been primarily limited to specialists. We propose a Business Process Transformation Wizard as a tool to bridge this gap. This enables users to easily ...
Chemical Physics Letters, 1997
... Data 10 Suppl. 1 (1981). [4] DL Baulch, RA Cox, RF Hampton Jr., JA Kerr, J. Troe, RT Watson, ... more ... Data 10 Suppl. 1 (1981). [4] DL Baulch, RA Cox, RF Hampton Jr., JA Kerr, J. Troe, RT Watson, J. Phys. Chem. Ref. ... [16] K. Nobusada, K. Moribayashi, and H. Nakamura, J. Chem. Soc., Faraday Trans., 93 (1997), in press. [17] SR Langhoff, ER Davidson, Int. J. Quantum Chem. ...
Journal of computational chemistry, Jan 30, 2016
Geometrical and electronic structures of the neutral and singly negatively charged Fe6 On and Fe7... more Geometrical and electronic structures of the neutral and singly negatively charged Fe6 On and Fe7 Om clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe6 O20 and Fe7 O24 , can be described as Fe(FeO4 )5 and Fe(FeO4 )6 or alternatively as [FeO5 ](FeO3 )5 and [FeO6 ](FeO3 )6 , respectively. The Fe6 O20 and Fe7 O24 clusters possess adiabatic electron affinities (EAad ) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO4 is an unique closed-shell superhalogen with the EAad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first FeOFe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 Å(3) of Fe6 to 2.47 Å(3) of Fe6 O20 and from 5....
Operations Research Letters, May 1, 2007
We show that base-stock levels first increase and then decrease as the standard deviation increas... more We show that base-stock levels first increase and then decrease as the standard deviation increases for a variety of nonnegative random variables with a given mean and provide a distribution-free upper bound for optimal base-stock levels that grows linearly with the standard deviation and then remains constant.
Proceedings of the 38th Conference, Dec 3, 2006
Proceedings - Frontiers in Education Conference, FIE, 2008
Louisiana Tech University's College of Engineering and Science has over ten years experience oper... more Louisiana Tech University's College of Engineering and Science has over ten years experience operating under an innovative multidisciplinary administrative structure which has created a supportive environment for numerous education reform initiatives. The traditional departmental structure was dismantled in favor of a much more flexible approach which has helped remove barriers between departments and promoted collaboration between engineering and science programs. The new administrative structure relies heavily on multidisciplinary teams and has been a key factor in the successful establishment of our first Integrated Engineering Curriculum in 1997, followed by our Integrated Science Curriculum in 2002. Other innovations implemented since that time include the first undergraduate nanosystems engineering degree program in the US; multidisciplinary design courses which include engineering, business, and technical writing students; a freshman enrichment program; the Living with the Lab curriculum (the most recent version of our Integrated Engineering Curriculum); and a program whereby engineering and science majors complete the Master of Arts in Teaching and become certified K-12 teachers. The College currently has $3.5 million in NSF funding for STEM projects. Much of the lasting success of these education reform efforts can be attributed to the supportive, interdisciplinary approaches the College uses in all of its core functions, including undergraduate education, research, and graduate education.
The Journal of Physical Chemistry C, 2012
Carbon chemisorption on iron nanoparticles at small carbon coverage has been studied by using a F... more Carbon chemisorption on iron nanoparticles at small carbon coverage has been studied by using a Fe 13 particle as a model because it possesses a nearly icosahedral geometry, and complications with additional effects associated with the surface inhomogeneity do not arise. The electronic and geometrical structures of Fe 13 C n are computed for n = 0−20 using an all-electron density functional theory with generalized gradient approximation and a rather large basis set. It is found that the energetically preferred structures correspond to the formation of carbon dimers up to Fe 13 C 12 and trimers up to Fe 13 C 18 in octahedral configurations of the dimers and trimers with the Fe 13 cluster being endohedral. The trend for the formation of carbon tetramers breaks at Fe 13 C 20. We found that the dependence of the total energy on the total spin is nearly the same for Fe 13 and Fe 13 C 8. When the number of chemisorbed carbon atoms exceeds 6, chemisorption quenches the total magnetic moment to 36 μ B from the value of 44 μ B in the ground-state Fe 13 cluster. We used natural atomic orbital populations to understand why the quenching does not depend on the number of chemisorbed atoms. Free C n species were reoptimized at the same level of theory to calculate the dissociation energies of C n and Fe 13 C n. It is found that the largest fragmentation energy of 12 eV belongs to the Fe 13 C 12 → Fe 13 + C 12 channel. Finally, we found that atomization energies for the carbon chemisorbed on the iron particle are larger by approximately 10 eV than atomization energies of the corresponding free carbon particles, which can be related to the catalytic strength of the Fe 13 particle. 49 total number reached 20, which is the number of triangular faces 50 in the Fe 13 icosahedral cluster. These faces are expected to be the 51 preferred bonding sites according to the electron localization 52 function (ELF) study 18 performed for Fe 4. Indeed, our computa-53 tional studies have shown that the face attachment of O or N to 54 Fe 4 and Fe 6 clusters 19,20 as well as C to a Fe 4 cluster 21 is preferred 55 when the number of carbon atoms is small. 56 Our computations on Fe 13 C n clusters (n = 1−20) are 57 performed using an all-electron DFT method with generalized 58 gradient approximation and a rather large basis set. We optimized 59 also the ground-state C n species (n = 2−20) at the same level of 60 theory so that the energetics of the carbon−carbon binding in the 61 gas phase could be compared to that in the presence of an Fe 13 62 particle. To gain insight into the carbon chemisorption 63 dependence on the spin multiplicity, we performed optimizations 64 of Fe 13 and Fe 13 C 8 in the whole range of the spin multiplicities 65 from 1 to 47. 66 Small precursors of these carbon allotropes were the subject 67 of numerous experimental and theoretical investigations. Smalley
The Journal of Chemical Physics, 2013
The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn... more The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni13, Cu13, Zn12, and Zn13 are found to be different from the geometries of the corresponding neutral parents. The computed ionization energies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M13 and M13+ clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 μB. Exceptions are found only fo...
American Journal of Infection Control, 2006
Background: Routine surveillance of nosocomial infections has become an integral part of infectio... more Background: Routine surveillance of nosocomial infections has become an integral part of infection control and quality assurance in US hospitals. Methods: As part of the International Nosocomial Infection Control Consortium, we performed a prospective nosocomial infection surveillance cohort study in 5 adult intensive care units of 4 Mexican public hospitals using the Centers for Disease Control and Prevention National Nosocomial Infections Surveillance system definitions. Site-specific nosocomial infection rates were calculated. Results: The overall nosocomial infection rate was 24.4% (257/1055) and 39.0 (257/6590) per 1000 patient days. The most common infection was catheter-associated bloodstream infection, 57.98% (149/257), followed by ventilator-associated pneumonia, 20.23% (52/257), and catheter-associated urinary tract infection, 21.79% (56/257). The overall rate of catheter-associated bloodstream infections was 23.1 per 1000 device-days (149/6450); ventilator-associated pneumonia rate was 21.8 per 1000 device-days (52/2390); and catheter-associated urinary tract infection rate was 13.4 per 1000 device-days (56/4184). Conclusion: Our rates are similar to other hospitals of Latin America and higher than US hospitals.
The Journal of Physical Chemistry A, 2003
Bond dissociation energies for the hypofluorous acid (HOF) system and an anharmonic force field f... more Bond dissociation energies for the hypofluorous acid (HOF) system and an anharmonic force field for HOF are obtained from ab initio energies at the CCSD(T)/CBS level of theory, where the complete basis set (CBS) limit energies are obtained by extrapolating CCSD(T)/aug-cc-pVnZ (n) 2, 3, and 4) energies. The effects of including core-valence correlation and scalar relativistic effects on the thermochemical and spectroscopic properties are investigated. The results are compared to available experimental results including recent reevaluations of the properties of OF and OH. Quartic force fields are calculated at each level of theory and basis set used. Excellent agreement between experimental and calculated properties is obtained in most cases, but a few prominent and large differences in rotation-vibration coupling constants and a few force constants are observed. In these cases, our results are consistent with other, high-level, ab initio evaluations of these properties. Given the ability of large basis set CCSD(T) calculations to yield accurate results for a wide range of molecular parameters, these differences suggest that experimental results may benefit from reexamination in some cases. A new recommendation for the 0 K enthalpy of formation of HOF, ∆H°f ,0K)-20.02 (0.25 kcal/mol, is presented based on a careful analysis of recent experimental data and is supported by the high-level ab initio calculations presented in this work.
The Journal of Organic Chemistry, 2007
The influence of temperature and solvent effects on the reduction and amination mechanisms of iod... more The influence of temperature and solvent effects on the reduction and amination mechanisms of iodomethane by lithium N,N-diisopropylaminoborohydride (iPr-LAB) was examined in varying concentrations of THF and dioxane. The reactions of benzyl chloride and trimethylsilyl chloride with iPr-LAB in THF were also studied. The amination of iodomethane is favored over reduction at low and room temperatures in pure THF and with increasing the amount of dioxane in THF. At higher temperatures, the reduction reaction appears to compete with the amination. In dioxane solvent, however, iodomethane yields exclusively the amination product regardless of temperature. On the other hand, reduction by iPr-LAB to the aminoborane is the only product observed in THF when benzyl chloride and trimethylsilyl chloride are used. To understand the solvent effects on the product distribution, ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane and bromomethane by lithium dimethylaminoborohydride (LAB) in THF and dioxane. The results of these calculations show that the relative reaction barrier heights are significantly affected by the nature of the coordinated solvent molecule and thus lend support to the experimental observations.
The Journal of Organic Chemistry, 2005
Journal of Chemical Education, 1994
Drooram disks 3 5 n or 5 25 in ; 1 free a & contamng sir.ctu& from Broo<naven hatonal Laooralory ... more Drooram disks 3 5 n or 5 25 in ; 1 free a & contamng sir.ctu& from Broo<naven hatonal Laooralory Prole n Data Ban6 Man-al 303 pp F gs ana Cnans, OJCA Reference 36 pp ] The meat advances in the Dower of micro~raeessors has made it quite practical to use relatively inexpensive personal computers for demonstrating, teaching, and exploring the principles of molecular structure and banding. Considering the pedagogic value of constructing, optimizing, and manipulating the structure of a molecule an a computer, it is tempting to say that such exercises must be an integral part of any advanced undergraduate or graduate course dealing with these topics. The MOBYMolecular Modelling on the PC version 1.5 is intended for just this type of classroom or self-study activity MOBY, uf cuurse, permits rhe cdorful display .f molccules, sl,owtng the m m s n i pmnts, crrcles,or thc~rorns nnd hnndsm the .'ball-and.irwk' rrprtirntstion. Apart from thlri, the pn,L?um boasts a long and impressive list of features, and among them are geometry optimization based an force-field calculations, conformational analysis, molecular dynamics simulations, and semi-empirical quantum chemistry calculations based an the MNDO (1) and AM1 (2) algorithms. The user is given three modes of operation. The "normal" mode provides the full features of the package, and is the default. A "protocol" mode permits the recording of a demonstration or teaching session, which the third mode, "demo", plays back. The documentation consists of a 303-page manual with a good index and a Quick Reference guide. The installation was easy and involved no surprises. The program came with a free disk containing a few protein structures from the Protein Data Bank of Brookhaven National Laboratory. The protein structures were supplied in a sin& executable file BRKHVN.EXE. from which the actual .. srruernrc.; h a w r u be cxll-ncrrd by running the wrnmand BRKIfl'N H o w w w , thwr IS nn mentmn of thls fact trt the docurnrnratwn ur in toe "HEAlJ ME" file thdr suppuscdly contains w-Volume 71 Number
Natural Computing Series
Cluster geometry optimization is an important problem from the Chemistry area. Hybrid approaches ... more Cluster geometry optimization is an important problem from the Chemistry area. Hybrid approaches combining evolutionary algorithms and gradientdriven local search methods are one of the most efficient techniques to perform a meaningful exploration of the solution space to ensure the discovery of low energy geometries. Here we perform a comprehensive study on the locality properties of this approach to gain insight on the algorithm's strengths and weaknesses. The analysis is accomplished through the application of several static measures to randomly generated solutions in order to establish the main properties of an extended set of mutation and crossover operators. Locality analysis is complemented with additional results obtained from optimization runs. The combination of the outcomes allows us to propose a robust hybrid algorithm that is able to quickly discover the arrangement of the cluster's particles that correspond to optimal or near-optimal solutions.
Chemical Physics Letters, 2000
The Journal of Organic Chemistry, 2005
Gas-phase activation energies were calculated for three lithium enolate reactions by using severa... more Gas-phase activation energies were calculated for three lithium enolate reactions by using several different ab initio and density functional theory (DFT) methods to determine which levels of theory generate acceptable results. The reactions included an aldol-type addition of an enolate to an aldehyde, a proton transfer from an alcohol to a lithium enolate, and an S N 2 reaction of an enolate with chloromethane. For each reaction, the calculations were performed for both the monomeric and dimeric forms of the lithium enolate. It was found that transition state geometry optimization with B3LYP followed by single point MP2 calculations generally provided acceptable results compared to higher level ab initio methods.
The Journal of Chemical Physics, 1999
A new potential energy surface for the lowest electronic state of the O() + HCl system is present... more A new potential energy surface for the lowest electronic state of the O() + HCl system is presented. This surface is based on electronic energies calculated at the multireference configuration interaction level of theory with the Davidson correction (MR-CI+Q) using the Dunning cc-pVTZ one-electron basis sets. The ab initio energies thus obtained are scaled using the Scaled External Correlation (SEC) method of Brown and Truhlar. The SEC-scaled energies are fitted to a simple analytical expression to yield a potential energy surface which correlates the reactants O() + HCl() to the products OH() + Cl(). The reaction barrier on this surface lies at an O-H-Cl angle of 131.4 at an energy of 9.78 kcal/mol above the asymptotic O + HCl minimum. This barrier is 1.3 kcal/mol higher than that on the potential energy surface obtained by Koizumi, Schatz, and Gordon (KSG) [J. Chem. Phys. 95, 6421 (1991)] and 1.1 kcal/mol lower than the S2 surface of Ramachandran, Senekowitsch, and Wyatt (RSW) [J. Mol. Struct. (Theochem) 454, 307 (1998)]. The dynamics of the reaction O() + HCl () OH() + Cl on this potential surface is studied using quasi-classical trajectory (QCT) propagation and the results are compared to the experimental observations of
Lower bounds for the quadratic assignment problem (QAP) tend to deteriorate rapidly with the size... more Lower bounds for the quadratic assignment problem (QAP) tend to deteriorate rapidly with the size of the QAP. Recently, Resende, Ramakrishnan, and Drezner (1995) computed a linear programming based lower bound for the QAP using an interior point algorithm for linear programming to solve the linear programming relaxation of a classical integer programming forn~ulation of the QAP. That linear progralil can be viewed as a two-body interaction formulation. Those bounds were found to be the tightest for a large number of instances from QAPLIB, a library of QAP test problems. In this paper, we apply the same interior point approach to compute lower bounds derived from the three-body interaction formulation of Ramachandran and Pekny (1996). All instances from QAPLIB, having dimension up to n = 12, were solved. The new approach produces tight lower hounds (lower bounds equal to the optimal solution) for all instances tested. Attempts to solve the linear programming relaxations with CPLEX (primal simplex, dual simplex, and barrier interior point method) were successful only for the smallest instances (n 5 6 for the barrier method, n 5 7 for tlle primal simplex method, and n 5 8 for the dual simplex method).
In spite of many advances in business process modeling and simulation technologies, their adoptio... more In spite of many advances in business process modeling and simulation technologies, their adoption by the business analyst community has been primarily limited to specialists. We propose a Business Process Transformation Wizard as a tool to bridge this gap. This enables users to easily ...
Chemical Physics Letters, 1997
... Data 10 Suppl. 1 (1981). [4] DL Baulch, RA Cox, RF Hampton Jr., JA Kerr, J. Troe, RT Watson, ... more ... Data 10 Suppl. 1 (1981). [4] DL Baulch, RA Cox, RF Hampton Jr., JA Kerr, J. Troe, RT Watson, J. Phys. Chem. Ref. ... [16] K. Nobusada, K. Moribayashi, and H. Nakamura, J. Chem. Soc., Faraday Trans., 93 (1997), in press. [17] SR Langhoff, ER Davidson, Int. J. Quantum Chem. ...
Journal of computational chemistry, Jan 30, 2016
Geometrical and electronic structures of the neutral and singly negatively charged Fe6 On and Fe7... more Geometrical and electronic structures of the neutral and singly negatively charged Fe6 On and Fe7 Om clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe6 O20 and Fe7 O24 , can be described as Fe(FeO4 )5 and Fe(FeO4 )6 or alternatively as [FeO5 ](FeO3 )5 and [FeO6 ](FeO3 )6 , respectively. The Fe6 O20 and Fe7 O24 clusters possess adiabatic electron affinities (EAad ) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO4 is an unique closed-shell superhalogen with the EAad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first FeOFe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 Å(3) of Fe6 to 2.47 Å(3) of Fe6 O20 and from 5....
Operations Research Letters, May 1, 2007
We show that base-stock levels first increase and then decrease as the standard deviation increas... more We show that base-stock levels first increase and then decrease as the standard deviation increases for a variety of nonnegative random variables with a given mean and provide a distribution-free upper bound for optimal base-stock levels that grows linearly with the standard deviation and then remains constant.
Proceedings of the 38th Conference, Dec 3, 2006