MOLCAS is an ab initio

Ab initio quantum chemistry methods

Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term ab initiowas first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene.The background is described by Parr...

 computational chemistry

Computational chemistry

Computational chemistry is a branch of chemistry that uses principles of computer science to assist in solving chemical problems. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids...

 program, developed at Lund University

Lund University

Lund University , located in the city of Lund in the province of Scania, Sweden, is one of northern Europe's most prestigious universities and one of Scandinavia's largest institutions for education and research, frequently ranked among the world's top 100 universities...

 in collaboration with others. Focus in the program is placed on methods for calculating general electronic structures in molecular systems

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 in both ground

Ground state

The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...

 and excited state

Excited state

Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....

s. MOLCAS is, in particular, designed to study the potential surfaces of excited states. The current version of MOLCAS is 7.4. Version 7.2 was reviewed in the Journal of the American Chemical Society

Journal of the American Chemical Society

The Journal of the American Chemical Society is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the Journal of Analytical and Applied Chemistry and the American Chemical Journal...

.

The program covers a wide range of features, including:

• Ab initio Hartree-Fock
  Hartree-Fock
  In computational physics and chemistry, the Hartree–Fock method is an approximate method for the determination of the ground-state wave function and ground-state energy of a quantum many-body system....
  
   (HF), Density functional theory
  Density functional theory
  Density functional theory is a quantum mechanical modelling method used in physics and chemistry to investigate the electronic structure of many-body systems, in particular atoms, molecules, and the condensed phases. With this theory, the properties of a many-electron system can be determined by...
  
   (DFT), second order Møller-Plesset perturbation theory
  Møller-Plesset perturbation theory
  Møller–Plesset perturbation theory is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...
  
  , MCSCF
  Multi-configurational self-consistent field
  Multi-configurational self-consistent field is a method in quantum chemistry used to generate qualitatively correct reference states of molecules in cases where Hartree–Fock and density functional theory are not adequate...
  
  , MRCI
  Multireference configuration interaction
  In quantum chemistry, the multireference configuration interaction method consists in a configuration interaction expansion of the eigenstates of the electronic molecular Hamiltonian in a set of Slater determinants which correspond to excitations of the ground state electronic configuration but...
  
  , CC
  Coupled cluster
  Coupled cluster is a numerical technique used for describing many-body systems. Its most common use is as one of several quantum chemical post-Hartree–Fock ab initio quantum chemistry methods in the field of computational chemistry...
  
   , CASPT2 wavefunctions and energies
• Analytic gradient geometry optimization based on HF, DFT, CASSCF, and RASSCF wavefunctions
• Choleski decomposition (CD)
  Cholesky decomposition
  In linear algebra, the Cholesky decomposition or Cholesky triangle is a decomposition of a Hermitian, positive-definite matrix into the product of a lower triangular matrix and its conjugate transpose. It was discovered by André-Louis Cholesky for real matrices...
  
   and Resolution of the identity (RI) techniques for HF, DFT, CASSCF, CC, MBPT2, and CASPT2.
• On-the-fly auxiliary basis function technique, aCD and acCD.
• CD/RI gradients for "pure" DFT functionals.
• Numerical gradient geometry optimization based on CASPT2 wavefunctions.
• Excited state energies for all wavefunctions, and excited optimized geometries from state averaged CASSCF wavefunctions.
• Transition properties in excited states calculated at the CASSCF/RASSCF level, using a unique RASSCF State Interaction Method.
• Solvent effects can be treated by the Onsager spherical cavity model or Polarizable continuum model
  Polarizable continuum model
  The polarizable continuum model is a commonly used method in computational chemistry to model solvation effects. If it were necessary to consider each solvent molecule as a separate molecule, the computational cost of modeling a solvent-mediated chemical reaction would grow prohibitively high...
  
   (PCM).
• Combined QM and molecular mechanics
  Molecular mechanics
  Molecular mechanics uses Newtonian mechanics to model molecular systems. The potential energy of all systems in molecular mechanics is calculated using force fields...
  
   calculations for systems such as proteins and molecular clusters.
• The NEMO procedure for creating intermolecular force fields for MC/MD simulations; these force fields include electrostatics, induction, dispersion, and exchange-repulsion terms, and are based on calculations for individual molecules.
• The Molcas INput Generator (MING) is a GUI for alternative graphical generation of MOLCAS input.

See also

External links

• MOLCAS collaboration map