libcint FFI Bindings and Wrapper

This project contains libcint (C language) FFI bindings, wrapper and build-from-source.

libcint is a C library for GTO (gaussian-type orbital) electronic integral, can be applied in computational chemistry, and has already been applied extensively in PySCF.

Resources	Badges
Crate
API Document
FFI Binding (libcint)	v6.1.2
FFI Binding (qcint)	v6.1.2
ECP Source Code (PySCF)	v2.9.0

This crate is not official bindgen project, nither libcint, PySCF, nor REST. It is originally intended to be some pioneer work for possible future development of rest_libcint wrapper.

Minimal Example

The most important function is CInt::integrate and CInt::integrate_row_major. It is somehow similar to PySCF's mol.intor(intor, aosym, shls_slice), but the user shall check output shape and strides. For more information on usage of crate libcint, we refer to API Documentation.

use libcint::prelude::*;

// This is for testing and development purpose only.
// For actual usage, you should initialize `CInt` with your own molecule data.
let cint_data: CInt = init_h2o_def2_tzvp();

// int1e_ipkin: the integral of kinetic energy operator with derivative on the first orbital

// [mu, nu, comp], column-major, same data memory layout to PySCF's 2/3-center intor
let (out, shape): (Vec<f64>, Vec<usize>) = cint_data.integrate("int1e_ipkin", None, None).into();
assert_eq!(shape, [43, 43, 3]);

// [comp, mu, nu], row-major, same shape to PySCF intor
let (out, shape): (Vec<f64>, Vec<usize>) = cint_data.integrate_row_major("int1e_ipkin", None, None).into();
assert_eq!(shape, [3, 43, 43]);

Installation and Cargo Features

Install with pre-compiled libcint.so (recommended)

If you have already compiled libcint.so, then put path of this shared library in CINT_DIR or LD_LIBRARY_PATH (or REST_EXT_DIR). Then you just use this library in your Cargo.toml file by

[dependencies]
libcint = { version = "0.1" }

Install and also build-from-source

If you have not compiled libcint.so or libcint.a, then you are suggested to use this library by specifying some cargo features:

[dependencies]
libcint = { version = "0.1", features = ["build_from_source", "static"] }

The source code will be automatically downloaded from github, and cargo will handle the building process.

If access to github is not available, you can use environment variable CINT_SRC to specify source mirror of sunqm/libcint or sunqm/qcint.

Cargo features

• Default features: None of any listed below (use library provided by system or user, using sunqm/libcint, dynamic linking, without F12 and 4c1e support).
• build_from_source: Trigger of C language library libcint building. This performs by CMake; source code will be automatically downloaded from github (if environment variable CINT_SRC not specified).
• static: Use static library for linking. This will require static link libcint.a, and dynamic link libquadmath.so.
• qcint: Use sunqm/qcint instead of sunqm/libcint. Some integrals will not be available if qcint does not supports that. This will also change URL source if cargo feature build_from_source specified.
• with_f12: Whether F12 integrals (int2e_stg, int2e_yp, etc.) are supported.
• with_4c1e: Whether 4c1e integrals (int4c1e, etc.) are supported.

Shell environment variables

• CINT_DIR, LD_LIBRARY_PATH, REST_EXT_DIR: Your compiled library path of libcint.so and libcint.a. This crate will try to find if this library is in directory root, or directory_root/lib. May override the library built by cargo feature build_from_source.
• CINT_SRC: Source of libcint or qcint (must be a git repository). Only works with cargo feature build_from_source.
• CINT_VIR: Version of libcint or qcint (e.g. v6.1.2, must starts with v prefix). Only works with cargo feature build_from_source.

50 lines RHF with Rust

This is a full example code to compute the RHF/def2-TZVP energy of H2O molecule, using

• This crate, libcint, as electronic integral library (corresponding to some parts of pyscf.gto);
• RSTSR as tensor library (corresponding to NumPy and SciPy).

You will see that except for import and preparation, the code with core algorithms is 27 lines (see also directory examples/h2o_rhf). For comparison, the same code in Python is 23 lines (see also pyscf_h2o_rhf.py).

use libcint::prelude::*;
use rstsr::prelude::*;

pub type Tsr = Tensor<f64, DeviceBLAS>;
pub type TsrView<'a> = TensorView<'a, f64, DeviceBLAS>;

/// Obtain integrals (in row-major, same to PySCF but reverse of libcint)
pub fn intor_row_major(cint_data: &CInt, intor: &str) -> Tsr {
    // use up all rayon available threads for tensor operations
    let device = DeviceBLAS::default();
    // intor, "s1", full_shls_slice
    let (out, shape) = cint_data.integrate(intor, None, None).into();
    // row-major by transposition of col-major shape
    rt::asarray((out, shape.f(), &device)).into_reverse_axes()
}

fn main() {
    let device = DeviceBLAS::default();
    // Assuming H2O/def2-TZVP data for `CInt` has been prepared
    let cint_data = init_h2o_def2_tzvp();

    /* #region rhf total energy algorithms */
    let atom_coords = {
        let coords = cint_data.atom_coords();
        let coords = coords.into_iter().flatten().collect::<Vec<f64>>();
        rt::asarray((coords, &device)).into_shape((-1, 3))
    };
    let atom_charges = rt::asarray((cint_data.atom_charges(), &device));
    let mut dist = rt::sci::cdist((atom_coords.view(), atom_coords.view()));
    dist.diagonal_mut(None).fill(f64::INFINITY);
    let eng_nuc = 0.5 * (&atom_charges * atom_charges.i((.., None)) / dist).sum();
    println!("Nuclear repulsion energy: {eng_nuc}");

    let hcore = intor_row_major(&cint_data, "int1e_kin") + intor_row_major(&cint_data, "int1e_nuc");
    let ovlp = intor_row_major(&cint_data, "int1e_ovlp");
    let int2e = intor_row_major(&cint_data, "int2e");
    let nocc = 5; // hardcoded for H2O, 5 occupied orbitals

    let mut dm = ovlp.zeros_like();
    for _ in 0..40 {
        // hardcoded SCF iterations
        let fock = &hcore + ((1.0_f64 * &int2e - 0.5_f64 * int2e.swapaxes(1, 2)) * &dm).sum_axes([-1, -2]);
        let (_, c) = rt::linalg::eigh((&fock, &ovlp)).into();
        dm = 2.0_f64 * c.i((.., ..nocc)) % c.i((.., ..nocc)).t();
    }
    let eng_scratch = &hcore + ((0.5_f64 * &int2e - 0.25_f64 * int2e.swapaxes(1, 2)) * &dm).sum_axes([-1, -2]);
    let eng_elec = (dm * &eng_scratch).sum();
    println!("Total elec energy: {eng_elec}");
    println!("Total RHF energy: {}", eng_nuc + eng_elec);
    /* #endregion */
}

License

This repository is licensed under Apache-2.0, the same to PySCF and REST.

• ECP part of code is directly copied and slightly modified from PySCF.
• Code for filling shell blocks of integrals is modified from an early version of rest_libcint.