# Most-cited Physics and Astronomy papers of 2021, with free PDFs

The 25 most-cited Physics and Astronomy research papers published in 2021, ranked by citations in OpenAlex, with their original abstracts and free PDFs where available.

1. [Efficient evaluation of electrostatic potential with computerized optimized code](https://nerdi.pages.dev/paper/W3195588649) · 2,667 citations
2. [DeepXDE: A Deep Learning Library for Solving Differential Equations](https://nerdi.pages.dev/paper/W2957969499) · 2,540 citations · Free PDF
3. [GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo during the First Half of the Third Observing Run](https://nerdi.pages.dev/paper/W3094812309) · 2,246 citations · Free PDF
4. [Understanding and Mitigating Gradient Flow Pathologies in Physics-Informed Neural Networks](https://nerdi.pages.dev/paper/W3200673624) · 2,055 citations
5. [Interaction Region Indicator: A Simple Real Space Function Clearly Revealing Both Chemical Bonds and Weak Interactions**](https://nerdi.pages.dev/paper/W3158379422) · 2,039 citations
6. [OPLS4: Improving Force Field Accuracy on Challenging Regimes of Chemical Space](https://nerdi.pages.dev/paper/W3167019654) · 2,016 citations
7. [Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3](https://nerdi.pages.dev/paper/W3111403703) · 1,995 citations · Free PDF
8. [In the realm of the Hubble tension—a review of solutions *](https://nerdi.pages.dev/paper/W3135850969) · 1,978 citations · Free PDF
9. [Planck 2018 results](https://nerdi.pages.dev/paper/W3193094654) · 1,853 citations
10. [Exceptional topology of non-Hermitian systems](https://nerdi.pages.dev/paper/W2994665279) · 1,719 citations · Free PDF
11. [Integrated photonics on thin-film lithium niobate](https://nerdi.pages.dev/paper/W3130725666) · 1,484 citations · Free PDF
12. [Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological implications from two decades of spectroscopic surveys at the Apache Point Observatory](https://nerdi.pages.dev/paper/W3043102132) · 1,340 citations · Free PDF
13. [Physics-Informed Neural Networks for Heat Transfer Problems](https://nerdi.pages.dev/paper/W3153200540) · 1,323 citations
14. [Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package](https://nerdi.pages.dev/paper/W3193988690) · 1,323 citations · Free PDF
15. [The Radius of PSR J0740+6620 from NICER and XMM-Newton Data](https://nerdi.pages.dev/paper/W3160077191) · 1,316 citations · Free PDF
16. [A NICER View of the Massive Pulsar PSR J0740+6620 Informed by Radio Timing and XMM-Newton Spectroscopy](https://nerdi.pages.dev/paper/W3160448096) · 1,275 citations · Free PDF
17. [r2SCAN-3c: A “Swiss army knife” composite electronic-structure method](https://nerdi.pages.dev/paper/W3129018228) · 1,109 citations
18. [Constraints on primordial black holes](https://nerdi.pages.dev/paper/W3007895520) · 1,107 citations · Free PDF
19. [X-ray computed tomography](https://nerdi.pages.dev/paper/W3046581697) · 1,089 citations · Free PDF
20. [Machine learning–accelerated computational fluid dynamics](https://nerdi.pages.dev/paper/W3128704025) · 1,046 citations · Free PDF
21. [Improved Constraints on Primordial Gravitational Waves using Planck , WMAP, and BICEP/ Keck Observations through the 2018 Observing Season](https://nerdi.pages.dev/paper/W3202102945) · 976 citations · Free PDF
22. [Refined Mass and Geometric Measurements of the High-mass PSR J0740+6620](https://nerdi.pages.dev/paper/W3152136163) · 951 citations · Free PDF
23. [Magnetically Driven Micro and Nanorobots](https://nerdi.pages.dev/paper/W3144873095) · 891 citations
24. [Metal Halide Perovskites for X-ray Imaging Scintillators and Detectors](https://nerdi.pages.dev/paper/W3126205838) · 889 citations
25. [Population Properties of Compact Objects from the Second LIGO–Virgo Gravitational-Wave Transient Catalog](https://nerdi.pages.dev/paper/W3161193838) · 889 citations · Free PDF

Canonical page: https://nerdi.pages.dev/papers/physics-and-astronomy/most-cited-2021