CHEMPS2(1)

📦
version 1.8.12 · 3 versions
, in debian bookworm, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

✨ CHEMPS2 ✨ — the manual, but make it make sense 💅

bestie, you've landed on the chemps2(1) manual page, and I'm about to walk you through it like we're in the group chat and you need to pass this exam. No cap. 💖

🌸 NAME 🌸

chemps2 — spin-adapted DMRG for ab initio quantum chemistry 🧚

🌈 SYNOPSIS 🌈

chemps2 [OPTION] ...

That's it. That's the whole vibe. Options, in, out, slay. ✨

🦋 DESCRIPTION 🦋

chemps2 is a scientific code that does spin-adapted density matrix renormalization group (DMRG) calculations for ab initio quantum chemistry fcidump files. Okay so basically — this method lets you get numerical accuracy in active spaces that are way beyond what full configuration interaction (FCI) can handle. It's giving "I can do what FCI can't." 👑

And it can return the active space 2-, 3-, and 4-RDM. Which means it's literally the perfect thing to swap in as the FCI solver inside complete active space self consistent field (CASSCF) and complete active space second order perturbation theory (CASPT2) methods. Main character energy fr fr.

The link to the user manual lives down in the SEE ALSO section, bestie — go look, iykyk. 🫶

🎀 OPTIONS 🎀

💫 SYMMETRY 💫

The conventions for the symmetry group and irrep numbers are the same as psi4, periodt:

                        |  0    1    2    3    4    5    6    7
               ---------|-----------------------------------------
               0 : c1   |  A
               1 : ci   |  Ag   Au
               2 : c2   |  A    B
               3 : cs   |  Ap   App
               4 : d2   |  A    B1   B2   B3
               5 : c2v  |  A1   A2   B1   B2
               6 : c2h  |  Ag   Bg   Au   Bu
               7 : d2h  |  Ag   B1g  B2g  B3g  Au   B1u  B2u  B3u

⭐ ARGUMENTS ⭐

  • -f, --file=inputfile — tell it which input file to read. 📂
  • -v, --version — prints the version of chemps2. 🏷️
  • -h, --help — shows you this help. 🆘

🌟 INPUT FILE 🌟

  • FCIDUMP = /path/to/fcidump — your FCIDUMP path. ⚠️ Heads up bestie: the orbital irreps in the FCIDUMP file follow the molpro convention!
  • GROUP = int — set the psi4 symmetry group number [0-7] that matches your FCIDUMP file. 🔢
  • MULTIPLICITY = int — overwrite the spin multiplicity [2S+1] from the FCIDUMP file. ✌️
  • NELECTRONS = int — overwrite the number of electrons from the FCIDUMP file. ⚡
  • IRREP = int — overwrite the target wavefunction irrep [0-7] from the FCIDUMP file (psi4 convention). 🎯
  • EXCITATION = int — picks which excitation to calculate. If it's zero, you get the ground state (default 0). 🌱
  • SWEEP_STATES = int,int,int — sets the number of reduced renormalized basis states for the successive sweep instructions (positive integers). 🔥
  • SWEEP_ENERGY_CONV = flt,flt,flt — sets the energy convergence that stops the successive sweep instructions (positive floats). 🛑
  • SWEEP_MAX_SWEEPS = int,int,int — sets the max number of sweeps for the successive sweep instructions (positive integers). 🔁
  • SWEEP_NOISE_PREFAC = flt,flt,flt — sets the noise prefactors for the successive sweep instructions (floats). 📣
  • SWEEP_DVDSON_RTOL = flt,flt,flt — sets the residual norm tolerance for the Davidson algorithm for the successive sweep instructions (positive floats). 🧮
  • NOCC = int,int,int,int — sets the number of occupied (external core) orbitals per irrep (psi4 irrep ordering). 🪑
  • NACT = int,int,int,int — sets the number of active orbitals per irrep (psi4 irrep ordering). ⚗️
  • NVIR = int,int,int,int — sets the number of virtual (secondary) orbitals per irrep (psi4 irrep ordering). 👻
  • MOLCAS_2RDM = /path/to/2rdm/output — when all orbitals are active orbitals, write out the 2-RDM in HDF5 format when specified (default unspecified). 📝
  • MOLCAS_3RDM = /path/to/3rdm/output — when all orbitals are active orbitals, write out the 3-RDM in HDF5 format when specified (default unspecified). 📝
  • MOLCAS_F4RDM = /path/to/f4rdm/output — when all orbitals are active orbitals, write out the 4-RDM contracted with the Fock operator in HDF5 format when specified (default unspecified). 📝
  • MOLCAS_FOCK = /path/to/fock/input — when all orbitals are active orbitals, read in this file containing the Fock operator (default unspecified). 📥
  • MOLCAS_FIEDLER = bool — when all orbitals are active orbitals, switch on orbital reordering based on the Fiedler vector of the exchange matrix (TRUE or FALSE; default FALSE). 🕸️
  • MOLCAS_ORDER = int,int,int,int — when all orbitals are active orbitals, provide a custom orbital reordering (default unspecified). ⚠️ When specified, this option takes precedence over MOLCAS_FIEDLER.
  • MOLCAS_OCC = int,int,int,int — when all orbitals are active orbitals, set initial guess to an ROHF determinant (default unspecified). The occupancy integers should be 0, 1 or 2 and the orbital ordering convention is FCIDUMP. 🧩
  • MOLCAS_MPS = bool — when all orbitals are active orbitals, switch on the creation of MPS checkpoints (TRUE or FALSE; default FALSE). 💾
  • MOLCAS_STATE_AVG = bool — switch on writing to disk of N-RDMs of intermediate roots (TRUE or FALSE; default FALSE). 💿
  • SCF_STATE_AVG = bool — switch on state-averaging (TRUE or FALSE; default FALSE). 🎚️
  • SCF_DIIS_THR = flt — switch on DIIS when the update norm is smaller than the given threshold (default 0.0). 📉
  • SCF_GRAD_THR = flt — gradient norm threshold for convergence of the DMRG-SCF orbital rotations (default 1e-6). 📐
  • SCF_MAX_ITER = int — sets the maximum number of DMRG-SCF iterations (default 100). 🔄
  • SCF_ACTIVE_SPACE = char — rotate the active space orbitals: no additional rotations (I), natural orbitals (N), localized and ordered orbitals (L), or ordered orbitals only (F) (default I). 🌀
  • SCF_MOLDEN = /path/to/molden — rotate the FCIDUMP orbitals to the DMRG-SCF occupied (external core), active, and virtual (secondary) orbitals. 🎨
  • CASPT2_CALC = bool — switch on the CASPT2 calculation (TRUE or FALSE; default FALSE). 🧪
  • CASPT2_ORBS = char — perform the DMRG calculation for the 4-RDM in the SCF_ACTIVE_SPACE orbitals (A) or in the pseudocanonical orbitals (P) (default A). 🛰️
  • CASPT2_IPEA = flt — ionization potential - electron affinity shift (default 0.0). ➖
  • CASPT2_IMAG = flt — imaginary level shift (default 0.0). 🌫️
  • CASPT2_CHECKPT = bool — create checkpoints to continue the CASPT2 4-RDM calculation over multiple runs (TRUE or FALSE; default FALSE). ⏸️
  • CASPT2_CUMUL = bool — use a cumulant approximation for the CASPT2 4-RDM and overwrite CASPT2_CHECKPT to FALSE (TRUE or FALSE; default FALSE). 🎁
  • PRINT_CORR = bool — print correlation functions (TRUE or FALSE; default FALSE). 🖨️
  • TMP_FOLDER = /path/to/tmp/folder — overwrite the tmp folder for the renormalized operators. With MPI, separate folders per process can (but do not have to) be used (default /tmp). 🗂️

🍓 EXAMPLE 🍓

Bestie, here's the whole run, verbatim, no edits:

 $ cd /tmp
 $ wget 'https://github.com/SebWouters/CheMPS2/raw/master/tests/matrixelements/N2.CCPVDZ.FCIDUMP'
 $ ls -al N2.CCPVDZ.FCIDUMP
 $ wget 'https://github.com/SebWouters/CheMPS2/raw/master/tests/test14.input'
 $ sed -i "s/path\/to/tmp/" test14.input
 $ cat test14.input
 $ chemps2 --file=test14.input

Obsessed with how clean that is. 🌸

👑 AUTHOR 👑

Written by Sebastian Wouters <sebastianwouters@gmail.com> 💌

💀 BUGS 💀

Reporting bugs: https://github.com/sebwouters/CheMPS2/issues — pls do report them, not me ignoring them 🙈

🔥 SEE ALSO 🔥

User manual: http://sebwouters.github.io/CheMPS2/index.html — the link from the DESCRIPTION, right where I promised it'd be 🫶

CheMPS2: a spin-adapted implementation of DMRG for ab initio quantum chemistry Copyright (C) 2013-2021 Sebastian Wouters
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License along
 with this program; if not, write to the Free Software Foundation, Inc.,
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

okay that's the whole page bestie, you ate that 💅 This was chemps2 version 1.8.12, dated 9 March 2022 — go be iconic with your DMRG, ily, bye! 🎀✨🦋

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