mirror of https://github.com/QMCPACK/qmcpack.git
81 lines
3.0 KiB
Plaintext
81 lines
3.0 KiB
Plaintext
Input files for a single helium atom.
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Simplest correlated wavefunction
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he_simple.xml
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The simplest possible wavefunction with electron correlation. It uses
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Slater Type Orbitals (STO) combined with a Pade form for the electron-electron
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Jastrow. The exponent of the STO should be fixed to the nuclear charge (Z=2)
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to cancel the -Z/r Coulomb term between the electrons and the nucleus (cusp
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condition). The Jastrow factor has one adjustable parameter (b).
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This runs Variational Monte Carlo (VMC) to compute the energy.
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Analyzing QMCPACK output
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------------------------
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One the output files, `He.s000.scalar.dat` contains scalar values, such as
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the local energy (first column). There should be one line of data for each
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block (the file should have `<blocks>` lines, plus one for the header).
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To analyze this data, use the `qmca` script (in the `nexus/bin` directory)
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on the scalar data file: `qmca He.s000.scalar.dat`. It should print out average
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values for each scalar along with an error estimate.
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The `qmca` script has other features (use `qmca -h` to see the help).
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For instance, to plot a trace of the local energy (matplotlib must be installed):
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`qmca --quantities LocalEnergy --trace He.s000.scalar.dat`.
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Optimizing variational parameters
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---------------------------------
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he_simple_opt.xml
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This file performs 10 iterations of the optimization loop. After running with
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QMCPACK, there should be a number of files in the directory with different
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series (the part the filename with `s000`, `s001`, etc.). Series 000-009
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are the optimization iterations, and series 010 is the final VMC run.
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The file `He.s009.opt.xml` contains the wavefunction with optimized parameters.
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The `qmca` script can plot the average energy for each run.
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Use `qmca --plot --quantities LocalEnergy He.s0*.scalar.dat`. Because this
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is a simple wavefunction with one parameter, only the first iteration really
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reduced the energy.
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Diffusion Monte Carlo
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---------------------
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he_simple_dmc.xml
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Runs Diffusion Monte Carlo (DMC). It first runs VMC to generate a set of
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walkers, and then performs DMC. There will be two series of output files - 000
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for the VMC and 001 for the DMC.
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Since there is only one electron of each spin, DMC should reproduce the exact
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non-relativistic ground state energy (-2.90372 Hartree).
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B-Splines
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---------
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he_bspline_jastrow.xml
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This uses a B-spline form for the electron-electron Jastrow correlation. There
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are four knots in the B-spline, and so four variational parameters. The input
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is set to optimize the B-spline coefficients.
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Orbitals from GAMESS
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--------------------
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he.inp
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he_from_gamess.xml
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The orbitals were obtained from the output of GAMESS. The GAMESS input file
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is he.inp.
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The `he_from_gamess.xml` input file does a VMC run by default. The optimization
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input code is commented out. Uncomment it and run to optimize the parameters.
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The number of samples (`<parameter name="samples">`) may need to be increased
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for better optimization convergence.
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