Siam Quantum (SQ) is an ab initio quantum chemistry program that uses quantum mechanics to determine the total energy and wave function of molecules within the framework of Hartee-Fock, Density Function Theory, and MP2 method.

Recent News

  • (July 25, 2017) The new GGA exchange functional See our manuscript at >>>  <<< T.Chachiyo and H.Chachiyo "Simple and accurate exchange energy for density functional theory"
    Posted Sep 19, 2017, 4:09 PM by teepanis
  • (August 15, 2016) The Chachiyo's Formula After making quite a buzz in July (see Physics Today's article "A simpler ingredient for a complex calculation", which kindly mentioned our research paper in JCP "Communication: Simple and ...
    Posted Nov 28, 2017, 12:49 PM by teepanis
  • (May 12, 2016) DFT is now avaiable Density Functional Theory is now available. Currently, LDA and Hybrid are supported such as Slater Exchange, VWN5, and HF+Slater hybrid. The results should be practically identical to the well ...
    Posted May 12, 2016, 4:12 AM by teepanis
  • (Feb 29, 2016) New Method for Finding Excitation Energies At last, Siam Quantum supports excited states, quantum molecular dynamics, and uniform external electric field. Please give the option -EXCITE, -QMD, and -EF=EX,EY,EZ a try. See Download ...
    Posted Mar 15, 2016, 12:55 PM by teepanis
  • (Feb 26, 2016) Seeking Collarboration We are seeking research collaboration to develop new methods to explore electronic properties of molecules, or to customize the Siam Quantum code to fit your prospective applications. Visiting scholars are ...
    Posted Feb 25, 2016, 7:06 PM by teepanis
Showing posts 1 - 5 of 17. View more »

  • Develop source code and documentation originally for academic purposes in order to introduce Thai students to the field of electronic structure calculations
  • Calculate Hartree-Fock, DFT,  and MP2 energies of molecules with the numerical results in excellent agreement with the standard quantum chemistry software such as GAMESS
  • DFT is available with various functionals such as the Dirac exchange, the VWN correlation, and the simplest yet accurate electron correlation energy, the so-called “Chachiyo's formula”.
  • Perform post SCF calculations such as electron density, molecular orbital, and dipole moment
  • Very Fast and support parallel calculation on multiple CPUs
  • Geometry optimization and simple population analysis
  • Quantum Molecular Dynamics
  • Support External Uniform Electric Field
  • Excited Energies and Oscillator Strength
  • Minimum Energy Crossing Point (MECP)
  • Free (GPL License), support both Linux and Windows


  • ESP Charge Fit
  • MP2 gradient


  • Spectroscopic parameter prediction
  • Support periodic system such crystal and carbon nanotube, especially at MP2 level
  • Graphic User Interface (GUI)
  • A book on electronic structure theory (in Thai language