Questions tagged [quantum-chemistry]

For questions about quantum chemistry.

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Analytical derivative method in ab initio molecular properties calculations

In order to relate results from quantum chemical calculations to experiment, it is essential to compute quantities that are directly available from measurements. Properties describe the "response&...
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How to build cartesian representations of spherical Gaussian basis functions?

I'm trying to code an integral library for my own QC software from scratch. I need to use the spherical basis functions like in any other popular program. So, a D basis function is supposed to make ...
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4 votes
1 answer
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Future and limitations of DFT

I'm a graduate student beginning research in condensed matter physics. Naturally, I am very interested in mathematics. I am aware that, in condensed matter physics, theorists employ tools from pure ...
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2 answers
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ORCA: Dipole moment of LiH from SP calculation

I calculate LiH with ORCA ...
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1 answer
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When is coupled cluster preferred over DFT?

I know that coupled cluster is considered to provide better accuracy than DFT, but I am not sure for which materials science applications or types of molecules that this higher accuracy is considered ...
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2 answers
216 views

Textbooks for electronic structure theory

Through this post I am looking to create a resourceful list of textbooks for any one interested in electronic structure theory. The focus here is to create mostly a mutually exclusive list of answers ...
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8 votes
1 answer
119 views

Basis sets optimized for CCSDT(Q) calculations

CCSDT(Q) and CCSDTQ calculations are extraordinarily expensive, both in terms of FLOP count and RAM capacity requirements, eg. CCSDTQ requires a computational effort that scales as ~$N^{10}$, where N ...
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ORCA: meaning of numbers in ORCA.out of MOLECULAR ORBITALS for STO-3G Lithium

For Lithium STO-3G basis set ...
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1 answer
111 views

List of programs for post-CCSD(T) calculations

Implementations of CCSD(T) are almost too numerous to list, but CCSDT and CCSDT(Q) are much more rare. I have compiled a list of such programs below, and I would be interested to hear if anyone is ...
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Repeated error in Quantum Espresso "Error in routine potinit (1)"

I have been trying to perform some calculations in Quantum espresso on mono-layer Borophene. Initially, I have optimized the structure which succeeds. Subsequently, I am trying to use this optimized ...
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1 answer
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For what DFT functional is useless to add D3 or similar corrections?

I would like to know for which DF is useless to add dispersion corrections. For example, I suppose that for the nonlocal density-based functionals such as wB97M-V it is unnecessary because the ...
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4 votes
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COSMO Model and Electric Potential on the Surface of the Cavity Inside Perfect Conductor

I am learning about COSMO model used in chemical engineering for calculating chemical potential and similiar quantites (actitvity coefficients) for solutes in solutions/mixtures. In the model, it is ...
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Sigma Profile in COSMO - RS model

As far as I understand, sigma profile in COSMO - RS is a probability distribution of screening charge density for certain molecular surface segment. In COSMO - RS, molecular surface area is segmented ...
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Segmentation fault with ORCA-3.0.1

I would like to use ORCA-3.0.1 under the following Linux version: 5.10.0-10-amd64 #1 SMP Debian 5.10.84-1 (2021-12-08) x86_64 GNU/Linux and Intel version ...
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Any molecular codes to calculate non-local susceptibility?

I am interested in calculating the non-interacting non-local susceptibility for simple molecules. In principle, if you have a single Slater determinant, then you should just take a sum over the ...
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6 votes
1 answer
116 views

Is it possible to calculate the dipole polarizability in the presence of a nonzero electric field?

One common way of calculating a dipole polarizability from electronic structure is by calculating the following derivative by finite difference: $$ \mathbf{\mu}=\left(\frac{\partial U}{\partial \...
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17 votes
4 answers
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I am considering to purchase a GPU. What calculations would need FP32, and what would need FP64?

I would like to know how to choose the best GPU on the basis of its FP32 or FP64 efficiency, depending on different types of simulations. In brief I would like to know what types of simulations work ...
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What prevents us from designing material or catalysts to meet the custom requirements? [closed]

From the perspective of physics, everything is made of atoms, ions, electrons, etc. Since we know the basic interaction between elementary particles, it might be possible to design customized ...
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How to predict protonation state of molecules in water?

I'm interested in predicting the protonation and tautomer state of organic molecules (typically CHNOS) at near pH 7 in water. I've used tools like Schrodinger's Epik / LigPrep before, but they ...
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3 answers
300 views

How to plot molecules with angles and bond lengths

There are many programs out there where you pass an XYZ coordinate file and the program will give you a visualization of the molecule. I want to make a plot like the one in the picture, with bond ...
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6 votes
1 answer
59 views

Transforming basis functions from Cartesian to speherical

I read the basis set from book A d-type GTO written in terms of the spherical functions has five components (Y2,2, Y2,1, Y2,0, Y2,1, Y2,2),but there appear to be six components in the Cartesian ...
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About LaCrO3 space group stability

I found two space groups of $\ce{LaCrO3}$ material Pnma and Pm-3m. If someone is familiar with this material, please help to understand which phase is more stable. what are the factors that determine ...
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5 votes
2 answers
171 views

How can I get started on DFT?

This question is simply: How can we use DFT in the field of electrochemistry? What are the best resources (Books, reviews, papers, software ...) to learn about using DFT in electrochemistry? ...
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The format and values provided by Basis Set Exchange

In this question and answers, I found that Basis Set Exchange provides information about the orbitals (e.g., the orbital exponents and contraction coefficients). For example, the following example is ...
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8 votes
1 answer
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What are the electronic steps and ionic steps in VASP?

I am getting confused about what the electronic step and ionic step are in VASP. I used to think that finishing the following loop one time is called an electronic step. but I am not sure how to ...
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10 votes
4 answers
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How can I find the parameters in a basis set?

I have a question about the basis functions of Gaussian. When the basis function is set (e.g., 6-31G), I would like to know the specific value of Gaussian's parameters for each atom. In particular, I ...
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214 views

Unrecognized or duplicated keyword error using ORCA

I wanted to run ORCA 5.0.2 with the following input: ...
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7 votes
1 answer
297 views

Where to find organic molecules atomic coordinates

I have found many organic molecule databases, such as PubChem or chEMBL. But they don't provide the atomic coordinates of each atom on the structure. I'm especially interested in organic molecules ...
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6 votes
0 answers
101 views

How do you perform parallelization of NEB-TS in ORCA? [closed]

I have tried running a NEB-TS calculation in orca with %pal nprocs 32, but I get an error saying ...
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10 votes
2 answers
273 views

Calculating the excited state dipole moment

I am trying to calculate the dipole moment of an excited state, using "Gaussian" software. My input commands were: ...
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7 votes
1 answer
67 views

What are the types of PT applied to electronic structure methods?

The motivation for this question is similar in nature to the series of questions on different methods : What are the types of SCF? What are the types of MCSCF? What are the types of Quantum Monte ...
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8 votes
2 answers
134 views

Vibrational frequencies results with GAMESS. Is it an equilibrium geometry?

A specific HESSIAN calculation carried out with GAMESS software presents this result: ...
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12 votes
0 answers
137 views

How may I calculate the "effective transfer integral" in free electronic-structure software?

I would like to calculate the following four quantities in a free electronic structure program: \begin{alignat}{2}\tag{1} e_1&=\langle\phi_1|H^{KS}|\phi_1\rangle,\\ e_2&=\langle\phi_2|H^{KS}|\...
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Implementing symmetry in MRCI calculation [closed]

I am running Multi Reference Configuration Interaction calculations for Aluminium Flouride molecule in its $A^1\Pi$ state interacting with Helium. For a complete Potential energy surface, I am doing ...
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8 votes
2 answers
148 views

Why are method developments and new implementations not done much in Gaussian?

While I have seen many papers in which Gaussian is used in calculations, I have not seen any paper in recent times where new methods are implemented in Gaussian. The latest paper I could find ...
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9 votes
1 answer
417 views

Why is the planewave codes ecosystem healthier on free/opensource software adoption, when compared to codes supporting atom-centered orbitals?

Regarding the branch of matter modeling that deals with electronic structure methods, I think we can divide it in two camps: Those who work mostly with planewave-based software, geared towards ...
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11 votes
3 answers
230 views

Quantum chemistry in external electrostatic field?

Which quantum chemistry methods can be used in an external electrostatic field? Also which software supports that? I'm interested in anything from semiempirical (eg XTB) to DFT (eg ωB97, B3LYP-D3) ...
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12 votes
1 answer
360 views

Comparing GAMESS, OpenMOLCAS and Psi4

Over the years many open-source ab initio packages have been developed and the diversity in subroutines, methods and portability (ability to interface with other software) is quite varied for ...
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5 votes
2 answers
184 views

SCF not converging during RHF/STO-3G geometry optimisation

I'm new in the field of QM methods and I've run into a problem for which I can't find a solution online. I have tried with different basis sets, I've raised the maximum number of iterations and number ...
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6 votes
0 answers
61 views

Orbital space clustering [closed]

I am interested in how the orbital space of a system can be partitioned into clusters. I read reading 'Cluster many-body expansion: A many-body expansion of the electron correlation energy about a ...
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6 votes
0 answers
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How to calculate energy gradient and Hessian with respect to only a few internal coordinates using Gaussian? [closed]

I would like to form the (numerical) gradient and the Hessian of the total electronic energy with respect only to a few internal coordinates (namely, the six intermolecular coordinates of a weakly ...
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8 votes
1 answer
192 views

Molecular orbitals and active space

During the same minute as asking this question, I also asked this at Quantum Computing SE. In Qiskit, each qubit corresponds to one spin orbital. For example, the $\ce{N2}$ molecule would have 10 ...
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15 votes
2 answers
371 views

What's the best quantum chemistry output parser for the command line?

This question is about tools like Open Babel. Are there any good command-line parsers for quantum chemistry program outputs? A good Python library could come in as a close second. I am interested e.g. ...
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7 votes
1 answer
215 views

How to extract transition density cube from .fch file in Gaussian?

I have been trying to extract the transition density cube of a simple molecule, $\ce{H_2O}$. I did a regular geometry optimization and then TD-DFT calculation with a keyword ...
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12 votes
2 answers
408 views

For DFT and Hartree-Fock, how can we know that we have a true minimum? Is there an equivalent to the "frequency analysis" for geometry optimization?

In a geometry optimisation, one can check if they have reached a minimum by checking the phonons. And to a certain extent, the global minimum can be confirmed by relaxing from different starting ...
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12 votes
2 answers
250 views

What are the references in multi-reference methods?

After reading What exactly is meant by 'multi-configurational' and 'multireference'? I still don't understand what the multiple "references" are. I understand that you can for example use a ...
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7 votes
0 answers
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How can I calculate the exchange energy for a molecule in PySCF? [closed]

I am trying to generate exchange energy separately in pyscf but didn't see a way to do that. For correlation energy, it's fairly simple but do you have any idea how to calculate exchange energy?
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11 votes
2 answers
304 views

DFT functionals from MP2 methods

I have heard people talk about DFT functionals built starting from MP2 corrections. Do you happen to have a reference I read about that from?
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8 votes
1 answer
481 views

Convert reduced density matrix from M.O. to A.O. basis

I am interested in converting the one-particle reduced matrix (rdm1) from the molecular orbital (M.O.) basis to the atomic orbital (A.O.) basis. Is the following method correct (in an identical ...
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8 votes
2 answers
67 views

Are there efficient open source implementations of electrostatic potential integrals?

We've had several questions regarding calculation and plotting of electron density. The electrostatic potential represents the interaction between a point charge at a given point $\mathbf{r}$ in a ...
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