konjkov/pycasino

Python realisation of Casino (QMC) program

Quantum Monte Carlo package

The Pycasino program implements some of the methods from the well-known Casino program.

Basic functionality

1. supported orbital file formats: gwfn.data, stowfn.data
2. using multi-determinant expansions
3. capable of doing 3-term Jastrow factor and 3-term Backflow
4. configuration-by-configuration (CBCS) and electron-by-electron (EBES) sampling
5. partial Ma CUSP correction (no rc optimization yet)
6. use only MPI parallelization
7. support VMC and DMC energy calculation, varmin and emin optimization

List of supported keywords in input file

General keywords:

• NEU, NED Number of electrons of up and down spin
• RUNTYPE Type of QMC calculation: vmc, vmc_dmc, vmc_opt
• TESTRUN If this flag is T then read input files, print information and stop
• ATOM_BASIS_TYPE The type of orbitals to be used: gaussian, slater-type

VMC keywords:

• VMC_EQUIL_NSTEP Number of equilibration steps
• VMC_NSTEP Number of VMC energy-evaluation steps
• VMC_DECORR_PERIOD Number of steps between VMC energy-evaluation moves
• VMC_NCONFIG_WRITE Number of VMC configurations stored for later use in DMC or optimization
• VMC_NBLOCK number of blocks into which the total VMC run is divided post-equilibration
• DTVMC VMC time step (size of trial steps in random walk)
• VMC_METHOD (1) - EBES (work in progress), (3) - CBCS.

Optimization keywords:

• OPT_CYCLES Number of optimization VMC cycles to perform
• OPT_METHOD Optimization method to use: varmin, emin
• OPT_JASTROW Optimize the Jastrow factor in wave-function optimization
• OPT_BACKFLOW Optimize backflow parameters in wave-function optimization
• OPT_DET_COEFF Optimize the coefficients of the determinants in wave-function optimization
• OPT_MAXEVAL Maximum number of evaluations of the variance during variance minimization (default 50)
• OPT_PLAN Allows specifying different parameters for each optimization cycle
• VM_REWEIGHT If set then the reweighted variance-minimization algorithm will be used, else the unreweighted algorithm will be used Unreweighted variance minimization is recommended
• EMIN_METHOD Energy minimization method to use: newton, linear (default), reconf

DMC keywords:

• DMC_TARGET_WEIGHT Target number of configurations in DMC
• DMC_EQUIL_NSTEP Number of DMC steps in equilibration
• DMC_STATS_NSTEP Number of DMC steps in statistics accumulation
• DMC EQUIL NBLOCK Number of blocks into which the DMC equilibration phase is divided
• DMC STATS NBLOCK Number of blocks into which the DMC statistics accumulation phase is divided
• DTDMC DMC time step
• DMC_METHOD (1) - EBES (work in progress), (2) - CBCS
• LIMDMC Set modifications to Green’s function in DMC. Only (4) Umrigar mods to drift velocity, Zen–Sorella–Alfè mods to energy
• ALIMIT Parameter required by DMC drift-velocity- and energy-limiting schemes
• NUCLEUS_GF_MODS This keyword is the switch for enabling the use of the modifications to the DMC Green’s function for the presence of bare nuclei
• EBEST_AV_WINDOW Averaging window for calculating the ground-state energy during equilibration (work in progress)

WFN definition keywords:

• BACKFLOW Turns on backflow corrections. Backflow parameters are read from correlation.data
• USE_JASTROW Use a wave function of the Slater-Jastrow form. The Jastrow factor is read from correlation.data
• USE_GJASTROW Use gjastrow Jastrow factor. This Jastrow factor is defined in a parameters.casl file (work in progress)

Cusp correction keywords:

• CUSP_CORRECTION When the cusp correction flag is activated, the s-type Gaussian basis functions centred on each atom are replaced within a small sphere by a function which ensures that the electron–nucleus cusp condition is obeyed
• CUSP_INFO If set then information about how cusp correction is done will be printed to the log-file
• CUSP_THRESHOLD If the magnitude of the s-component of a Gaussian orbital is less than this threshold then it will not be cusp corrected

Pseudopotential keywords:

• NON_LOCAL_GRID Selects the grid for nonlocal integration, can take values between 1 and 7, the default being 4
• LCUTOFFTOL This is used to define the cutoff radius for the local part of the pseudopotential, the default being 1e-5
• NLCUTOFFTOL This is used to define the cutoff radius for the nonlocal parts of the pseudopotential, the default being 1e-5