Water Optimization with TREXIO¶

This tutorial demonstrates a full wavefunction optimization (Jastrow + Orbitals) for Water (\(H_2O\)) using the TREXIO file format input. This represents the modern, streamlined workflow for CHAMP calculations.

System Configuration¶

Molecule: Water (\(H_2O\))
Source Format: TREXIO (HDF5)
Method: VMC Optimization (sr_n)
Optimization Targets: Jastrow factor + Orbital coefficients

Input File Setup¶

Input File: vmc_h2o_dft_optall.inp

%module general
    title           'H2O DFT calculation'
    pool            './pool/'
    mode            vmc_one_mpi
%endmodule

# Single command to load all wavefunction data
load trexio          H2O_DFT.hdf5

# Load Jastrow parameters
load jastrow         jastrow.dft_optimal_2body
load jastrow_der     jastrow.der

%module electrons
    nup           4
    nelec         8
%endmodule

%module optwf
    ioptwf        1       # Enable optimization
    ioptci        0       # Keep CI coefficients fixed (single determinant)
    ioptjas       1       # Optimize Jastrow
    ioptorb       1       # Optimize Orbitals

    method        'sr_n'  # Stochastic Reconfiguration
    ncore         0
    nextorb       100     # Number of external orbitals to use for rotation
    nblk_max      4000
    nopt_iter     1       # 1 iteration for testing (increase for production)
    sr_tau        0.05
    sr_eps        0.01
    sr_adiag      0.01
%endmodule

%module blocking_vmc
    vmc_nstep     20
    vmc_nblk      1000
%endmodule

Key Features¶

Compact Input: Geometry, Basis, Determinants, and Orbitals are all loaded via load trexio.
Orbital Optimization: ioptorb 1 allows relaxation of the DFT orbitals within the VMC variational principle.
DFT Starting Point: The input H2O_DFT.hdf5 contains orbitals generated from a DFT calculation.

Resources for this test can be found in the Water TREXIO CI Test folder.