CASINO

• Variational Monte Carlo. Wave function optimization achieved with variance minimization, accelerated variance minimization, energy minimization, and minimization of the mean absolute deviation of the set of local energies from the median.
• Fixed-node/fixed-phase diffusion Monte Carlo (pure or branching)
• Applicable to finite systems such as atoms and molecules and also to systems with periodic boundary conditions in 1, 2 or 3 dimensions (polymers, slabs/surfaces, crystalline solids) with any crystal structure.
• Capable of using "linear scaling" methods in which the time to move an electron scales linearly with the system size (though the time taken to get the answer to a specified error bar scales quadratically, which is still very good compared to high accuracy quantum chemistry methods).
• Perfect parallel efficiency on massively parallel machines of at least hundreds of thousands of cores for VMC, wave function optimization, and DMC (since version 2.8). See this article.

• Can exploit modern shared memory processor architectures and OpenMP multi-threading parallelization.
• Can be used with different types of particles and combinations of different particles.
• Real or complex wave functions.
• The code may use orbitals expanded in a variety of basis sets in the determinantal part of the many-electron trial wave function:
  (1) s, sp, p, d, f or g Gaussian basis functions centred on atoms or elsewhere (aperiodic or periodic systems) with cusp corrections in the case of all-electron calculations.
  (2) plane-waves (periodic systems)
  (3) blip functions, i.e., cubic splines on a regular grid (periodic systems)
  (4) Slater functions centred on atoms. (5) atomic calculations with numerical orbitals interpolated from a radial grid.
  
• Uses flexible Slater-Jastrow many-electron wave functions, where the Slater part may consist of multiple determinants.
• Backflow correlations (also in inhomogeneous systems).
• Pairing wave functions.
• It is linked to various one-electron packages via a generic interface for each basis set type, which allows us to use a variety of different software to generate trial wave functions via density functional theory or Hartree-Fock calculations. In certain cases (e.g. excited states) it is also desirable to generate multi-determinant trial wave functions via standard quantum chemistry methods such as CIS/CISD/TD-DFT/CASSCF methods. With Gaussian basis sets we have used the following programs to calculate trial wave functions:
  (1) CRYSTAL (95/98/03/06/09). DFT/HF for molecules and systems periodic in 1,2 or 3 dimensions.
  (2) GAUSSIAN (94/98/03/09). Huge quantum chemistry package for molecules.
  (3) TURBOMOLE
  (4) GAMESS-US
  (5) QCHEM (coming soon)
  For calculations with blip function or plane-wave basis sets we use the PWSCF (Quantum Espresso), ABINIT, CASTEP, or GP packages. For calculations with Slater basis sets we use the ADF program. Thus, any system that can be treated with any of the above programs can now in principle also be handled within QMC. Note that it is also planned at some stage to look at implementing links to other well-known DFT codes. If you wish to make a generous offer to assist with such projects, then please email Mike Towler, who will be pleased to hear from you.
• Non-local pseudopotentials with s, p, d non-locality, and core polarization potentials. Possibility to use Casula non-local scheme.
• Computation of ground and excited state energies.
• Computation of forces on atoms in VMC or DMC.
• Coupled DFT-DMC molecular dynamics calculations (with the PWSCF code).
• Computation of various expectation values such as pair correlation functions, density matrices, spin densities, localization tensors, dipole moments, and structure factors.
• Periodic Coulomb interactions computed either with standard Ewald methods or with our MPC (modified periodic Coulomb) interaction which is both faster than the Ewald method and exhibits smaller 'finite-size effects'. Twist averaging. New method based on structure factor implemented in CASINO 2.1.
• Spin-polarized calculations (e.g., of magnetic solids).
• Non-collinear spin systems (for a restricted set of cases)
• The code has been written entirely in standard-conforming Fortran95 using modern software design methods, and is supposed to be easy to use, easy to install, and easy to read and understand. It contains a self-documenting help system and comes with a helpful manual and examples.
• The distribution comes with a very large number of utilities and additional programs to help with analysis, running the code, and preparing the input.
• It is straightforward to mount CASINO across a variety of platforms (including workstations, weakly-linked clusters, massively parallel supercomputers, laptops, PCs, and probably Iphones and stuff). It uses the standard MPI functions to work on parallel machines, but will work without it on single processors (having its own 'fake' serial MPI library).
• It's way cooler than any other QMC code, especially the one that Lucas wrote.