Contributions

• the transcorrelated method
• the long range behaviour of 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....
  
   orbitals
  Molecular orbital
  In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
  
  
• semiclassical methods for vibrational energies
  Energy level
  A quantum mechanical system or particle that is bound -- that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels...
  
  
• the variational method
  Variational method (quantum mechanics)
  In quantum mechanics, the variational method is one way of finding approximations to the lowest energy eigenstate or ground state, and some excited states...
  
   for rovibrational wave-functions (in normal
  Normal mode
  A normal mode of an oscillating system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. The frequencies of the normal modes of a system are known as its natural frequencies or resonant frequencies...
  
   and internal coordinates)
• Full configuration interaction
  Full configuration interaction
  Full configuration interaction is a linear variational approach which provides numerically exact solutions to the electronic time-independent, non-relativistic Schrödinger equation....
  
   with Slater determinant
  Slater determinant
  In quantum mechanics, a Slater determinant is an expression that describes the wavefunction of a multi-fermionic system that satisfies anti-symmetry requirements and consequently the Pauli exclusion principle by changing sign upon exchange of fermions . It is named for its discoverer, John C...
  
  s (benchmark studies)
• convergence of the Møller-Plesset series
• the reaction path
  Reaction coordinate
  In chemistry, a reaction coordinate is an abstract one-dimensional coordinate which represents progress along a reaction pathway. It is usually a geometric parameter that changes during the conversion of one or more molecular entities....
  
   Hamiltonian
  Hamiltonian (quantum mechanics)
  In quantum mechanics, the Hamiltonian H, also Ȟ or Ĥ, is the operator corresponding to the total energy of the system. Its spectrum is the set of possible outcomes when one measures the total energy of a system...
  
  
• Anharmonic spectroscopic and thermodynamic properties using higher derivative methods
• Brueckner-doubles theory
• Open shell
  Open shell
  In the context of atomic orbitals, an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction. Atoms generally reach a noble gas configuration in a...
  
   Møller-Plesset theory
• frequency-dependent properties
• 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...
  
   : quadrature, new functionals and molecular properties.

Other Merits

• Fellow of the Royal Society, London (1990).
• Member of the International Academy of Quantum Molecular Science
  International Academy of Quantum Molecular Science
  The International Academy of Quantum Molecular Science is an international scientific learned society covering all applications of quantum theory to chemistry and chemical physics. It was created in Menton in 1967. The founding members were Raymond Daudel, Per-Olov Löwdin, Robert G. Parr, John...
  
  .