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https://github.com/konjkov/pycasino

Python realisation of Casino (QMC) program
https://github.com/konjkov/pycasino

mpi4py numba numpy python3 quantum-chemistry quantum-monte-carlo scipy

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Python realisation of Casino (QMC) program

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README 

        
# Quantum Monte Carlo package



The Pycasino is python implementation of the well-known [Casino](https://vallico.net/casinoqmc/) 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. MPI parallelization

7. support VMC and DMC energy calculation, varmin and emin optimization

8. pseudopotential



## 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, (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