Gaussian‐2 theory: Use of higher level correlation methods, quadratic configuration interaction geometries, and second‐order Mo/ller–Plesset zero‐point energies

1995 ◽  
Vol 103 (10) ◽  
pp. 4192-4200 ◽  
Author(s):  
Larry A. Curtiss ◽  
Krishnan Raghavachari ◽  
John A. Pople
Keyword(s):  
Configuration Interaction ◽  
Zero Point ◽  
Second Order ◽  
Correlation Methods ◽  
Theory Use

Superconducting Pairs in Clusters and in the Cu-O Plane

1999 ◽  
Vol 13 (09n10) ◽  
pp. 1195-1200
Author(s):  
Michele Cini ◽  
Adalberto Balzarotti ◽  
Gianluca Stefanucci
Keyword(s):  
Configuration Interaction ◽  
Interaction Mechanism ◽  
Second Order ◽  
Flux Quantization ◽  
Spin Flip ◽  
Full Plane ◽  
Superconducting Pairing ◽  
Exact Diagonalisation

Recently, by exact diagonalisation methods, we reported superconducting pairing and flux quantization in Cu-O Hubbard clusters of up to 21 atoms. The pairing is due to a configuration interaction mechanism driven by symmetry, and arises when the least bound holes have vanishing mutual repulsion ( W =0 pairs). The second-order, spin-flip interaction leads to a net attraction for the singlet and repulsion for the triplet. Here we show that electron bound pairs also exist and show similar flux quantization properties. Then, we extend the theory of pairing to the full plane and to all orders.

Gaussian-3X (G3X) theory: Use of improved geometries, zero-point energies, and Hartree–Fock basis sets

2001 ◽  
Vol 114 (1) ◽  
pp. 108 ◽  
Author(s):  
Larry A. Curtiss ◽  
Paul C. Redfern ◽  
Krishnan Raghavachari ◽  
John A. Pople
Keyword(s):  
Zero Point ◽  
Basis Sets ◽  
Hartree Fock ◽  
Theory Use

scholarly journals Quantum Package 2.0: An Open-Source Determinant-Driven Suite of Programs

2019 ◽  
Author(s):  
Yann Garniron ◽  
Thomas Applencourt ◽  
Kevin Gasperich ◽  
Anouar Benali ◽  
Anthony Ferte ◽  
...  
Keyword(s):  
Open Source ◽  
Configuration Interaction ◽  
Density Functional ◽  
Collaborative Work ◽  
Second Order ◽  
Functional Theory ◽  
Code Generator ◽  
Stochastic Version ◽  
Reference Space ◽  
Full Ci

<div> <div> <div> <p> </p><div> <div> <div> <p>Quantum Package is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinant-driven selected configuration interaction (sCI) methods and multi-reference second-order perturbation theory (PT2). The determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater method- ological freedoms. The sCI method implemented in Quantum Package is based on the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm which complements the variational sCI energy with a PT2 correction. Additional external plugins have been recently added to perform calculations with multireference coupled cluster theory and range-separated density-functional theory. All the programs are developed with the IRPF90 code generator, which simplifies collaborative work and the development of new features. Quantum Package strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and efficient as possible on modern supercomputer architectures. Currently, the code enables, routinely, to realize runs on roughly 2 000 CPU cores, with tens of millions of determinants in the reference space. Moreover, we have been able to push up to 12 288 cores in order to test its parallel efficiency. In the present manuscript, we also introduce some key new developments: i) a renormalized second-order perturbative correction for efficient extrapolation to the full CI limit, and ii) a stochastic version of the CIPSI selection performed simultaneously to the PT2 calculation at no extra cost. </p> </div> </div> </div> </div> </div> </div>

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