Computational chemistry is a branch of chemistry that uses computer simulations to assist in solving chemical problems. It uses methods of theoretical chemistry incorporated into computer programs to calculate the structures and properties of molecules,groups of molecules,and solids. The importance of this subject stems from the fact that,with the exception of some relatively recent findings related to the hydrogen molecular ion,achieving an accurate quantum mechanical depiction of chemical systems analytically,or in a closed form,is not feasible. The complexity inherent in the many-body problem exacerbates the challenge of providing detailed descriptions of quantum mechanical systems. While computational results normally complement information obtained by chemical experiments,it can occasionally predict unobserved chemical phenomena.
In theoretical physics,quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton,neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory,with symmetry group SU(3). The QCD analog of electric charge is a property called color. Gluons are the force carriers of the theory,just as photons are for the electromagnetic force in quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. A large body of experimental evidence for QCD has been gathered over the years.
In physics,lattice gauge theory is the study of gauge theories on a spacetime that has been discretized into a lattice.
In physics,an effective field theory is a type of approximation,or effective theory,for an underlying physical theory,such as a quantum field theory or a statistical mechanics model. An effective field theory includes the appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale or energy scale,while ignoring substructure and degrees of freedom at shorter distances. Intuitively,one averages over the behavior of the underlying theory at shorter length scales to derive what is hoped to be a simplified model at longer length scales. Effective field theories typically work best when there is a large separation between length scale of interest and the length scale of the underlying dynamics. Effective field theories have found use in particle physics,statistical mechanics,condensed matter physics,general relativity,and hydrodynamics. They simplify calculations,and allow treatment of dissipation and radiation effects.
Carbon-12 (12C) is the most abundant of the two stable isotopes of carbon,amounting to 98.93% of element carbon on Earth;its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured,thus,its atomic mass is exactly 12 daltons by definition. Carbon-12 is composed of 6 protons,6 neutrons,and 6 electrons.
Lattice QCD is a well-established non-perturbative approach to solving the quantum chromodynamics (QCD) theory of quarks and gluons. It is a lattice gauge theory formulated on a grid or lattice of points in space and time. When the size of the lattice is taken infinitely large and its sites infinitesimally close to each other,the continuum QCD is recovered.
The Vienna Ab initio Simulation Package,better known as VASP,is a package written primarily in Fortran for performing ab initio quantum mechanical calculations using either Vanderbilt pseudopotentials,or the projector augmented wave method,and a plane wave basis set. The basic methodology is density functional theory (DFT),but the code also allows use of post-DFT corrections such as hybrid functionals mixing DFT and Hartree–Fock exchange,many-body perturbation theory and dynamical electronic correlations within the random phase approximation (RPA) and MP2.
A three-body force is a force that does not exist in a system of two objects but appears in a three-body system. In general,if the behaviour of a system of more than two objects cannot be described by the two-body interactions between all possible pairs,as a first approximation,the deviation is mainly due to a three-body force.
Jaguar is a computer software package used for ab initio quantum chemistry calculations for both gas and solution phases. It is commercial software marketed by the company Schrödinger. The program was originated in research groups of Richard Friesner and William Goddard and was initially called PS-GVB.
Car–Parrinello molecular dynamics or CPMD refers to either a method used in molecular dynamics or the computational chemistry software package used to implement this method.
Beryllium-8 is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 8.19×10−17 seconds. This has important ramifications in stellar nucleosynthesis as it creates a bottleneck in the creation of heavier chemical elements. The properties of 8Be have also led to speculation on the fine tuning of the Universe,and theoretical investigations on cosmological evolution had 8Be been stable.
In applied mathematics,the numerical sign problem is the problem of numerically evaluating the integral of a highly oscillatory function of a large number of variables. Numerical methods fail because of the near-cancellation of the positive and negative contributions to the integral. Each has to be integrated to very high precision in order for their difference to be obtained with useful accuracy.
Francisco JoséYnduráin Muñoz was a Spanish theoretical physicist. He founded the particle physics research group that became the Department of Theoretical Physics at the Autonomous University of Madrid,where he was a Professor. He was described by his colleagues as "a scientist that always searched for excellence in research".
CP2K is a freely available (GPL) quantum chemistry and solid state physics program package,written in Fortran 2008,to perform atomistic simulations of solid state,liquid,molecular,periodic,material,crystal,and biological systems. It provides a general framework for different methods:density functional theory (DFT) using a mixed Gaussian and plane waves approach (GPW) via LDA,GGA,MP2,or RPA levels of theory,classical pair and many-body potentials,semi-empirical and tight-binding Hamiltonians,as well as Quantum Mechanics/Molecular Mechanics (QM/MM) hybrid schemes relying on the Gaussian Expansion of the Electrostatic Potential (GEEP). The Gaussian and Augmented Plane Waves method (GAPW) as an extension of the GPW method allows for all-electron calculations. CP2K can do simulations of molecular dynamics,metadynamics,Monte Carlo,Ehrenfest dynamics,vibrational analysis,core level spectroscopy,energy minimization,and transition state optimization using NEB or dimer method.
Heat transfer physics describes the kinetics of energy storage,transport,and energy transformation by principal energy carriers:phonons,electrons,fluid particles,and photons. Heat is thermal energy stored in temperature-dependent motion of particles including electrons,atomic nuclei,individual atoms,and molecules. Heat is transferred to and from matter by the principal energy carriers. The state of energy stored within matter,or transported by the carriers,is described by a combination of classical and quantum statistical mechanics. The energy is different made (converted) among various carriers. The heat transfer processes are governed by the rates at which various related physical phenomena occur,such as the rate of particle collisions in classical mechanics. These various states and kinetics determine the heat transfer,i.e.,the net rate of energy storage or transport. Governing these process from the atomic level to macroscale are the laws of thermodynamics,including conservation of energy.
The light-front quantization of quantum field theories provides a useful alternative to ordinary equal-time quantization. In particular,it can lead to a relativistic description of bound systems in terms of quantum-mechanical wave functions. The quantization is based on the choice of light-front coordinates,where plays the role of time and the corresponding spatial coordinate is . Here, is the ordinary time, is a Cartesian coordinate,and is the speed of light. The other two Cartesian coordinates, and ,are untouched and often called transverse or perpendicular,denoted by symbols of the type . The choice of the frame of reference where the time and -axis are defined can be left unspecified in an exactly soluble relativistic theory,but in practical calculations some choices may be more suitable than others. The basic formalism is discussed elsewhere.
In nuclear physics,ab initio methods seek to describe the atomic nucleus from the bottom up by solving the non-relativistic Schrödinger equation for all constituent nucleons and the forces between them. This is done either exactly for very light nuclei or by employing certain well-controlled approximations for heavier nuclei. Ab initio methods constitute a more fundamental approach compared to e.g. the nuclear shell model. Recent progress has enabled ab initio treatment of heavier nuclei such as nickel.
James P. Vary is an American theoretical physicist and professor at the Iowa State University,specializing in nuclear theory with an emphasis on "ab initio" solutions of quantum many-particle systems and light-front quantum field theory.
G. Peter Lepage is a Canadian American theoretical physicist and an academic administrator. He was the Harold Tanner Dean of the College of Arts and Sciences at Cornell University from 2003 to 2013.
Zoltan Fodor is a Hungarian-German theoretical particle physicist,best known for his works in lattice quantum chromodynamics.
