## Wednesday, May 28, 2008

### molcas

http://www.teokem.lu.se/molcas/

MOLCAS-7 is the latest version of the MOLCAS quantum chemistry software program. It has been released for distribution in the summer of 2007. MOLCAS-7 is a quantum chemistry code that allows studies of molecular systems using a variety of quantum chemical models ranging from SCF/DFT to coupled cluster and multiconfigurational SCF (RASSCF) with dynamical electron correlation treated with multi-reference CI or second order perturbation theory (MS-CASPT2). MOLCAS emphasizes the multiconfigurational approach for quantum chemical calculations, which allows studies of systems where a single configuration does not give a good representation of the electronic structure. Examples are excited states, transition states for chemical reactions, heavy element systems (transition metals, lanthanides, actinides), and much more.

Molcas is distributed as a source code with the set of configuration files for different hardware and compilers. In fact, Molcas is running under almost all Unix and Linux platforms, and also under MS Windows and Mac OS 10 operating systems.

## Excited States and Electronic Spectra

MOLCAS is in particular designed to study potential surfaces for excited states.
• Energies may be obtained using all the wave function methods. Geometry optimization is possible also for state average RASSCF energies.
• Transition properties are computed at the RASSCF level using the RASSCF State Interaction Method, which is unique to the MOLCAS program.
• The same code can also be used to compute spin-orbit coupling using a effective one-electron SO Hamiltonian and so called Atomic Mean Field Integrals (AMFI).
• Automatic search at the RASSCF level for energy barriers, conical intersections, etc on excited state surfaces.
• Vibrationally resolved electronic spectra may be obtained using the MULA code for computing transition dipole moments between harmonic vibrational levels of two electronic states.