If a Quantum ESPRESSO pw.x self-consistent-field (SCF) calculation is slow, oscillates, or stops without converging, first check the structure and input, then match a change to the failure pattern. For metallic systems, review occupations, bands, broadening, and k-points; for oscillatory charge density, test gentler mixing. There is no universally reliable setting: compare changes one at a time and watch the convergence history.
Start by checking the model and input
Before changing mixing controls, verify that the calculation describes the intended system. Quantum ESPRESSO’s SCF troubleshooting guide warns that bad input often leads to poor convergence and specifically recommends checking the structure.
- Inspect the atomic positions, cell, species, and pseudopotential assignments for mistakes or implausible geometry.
- Check the electron count and number of bands (
nbnd). - Review the k-point mesh and relevant settings in
&SYSTEMand&ELECTRONS.
Mixing changes cannot reliably compensate for a malformed structure or incorrect calculation setup. Make sure the model is sound before tuning the SCF loop.
Check whether the system is metallic
Metallic and near-metallic systems can have occupation changes that make the SCF error fall and then rise again. The troubleshooting guide describes this pattern when the highest occupied and lowest unoccupied states exchange places, particularly with a sparse k-point mesh. It suggests adding some empty bands and a small broadening as possible remedies.
Free tools Windows power users keep installed
One-click scans. No signup required.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
Choose occupations for the calculation
The guide says occupations='fixed' works only for insulators with a gap, and recommends occupations='smearing' otherwise. It identifies 'tetrahedra' as an option for density-of-states calculations. Treat these as calculation-dependent choices rather than a blanket edit; changing occupations can affect how the calculation represents electronic states.
Review bands, broadening, and k-points together
If the system is metallic or nearly so, assess whether the band count leaves enough empty states and whether the broadening and k-point sampling are appropriate. For cannot bracket Ef, the guide notes that first-order Methfessel–Paxton smearing can be troublesome with very few k-points because the integrated density of states is not guaranteed to increase monotonically. It suggests Gaussian or Marzari–Vanderbilt–DeVita–Payne (cold) smearing as alternatives.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Stabilize oscillatory charge-density mixing
If the main symptom is a slow or unstable SCF cycle, test a smaller mixing_beta. The official troubleshooting guide and self-consistency FAQ give approximately 0.3 to 0.1 or smaller as a starting range. This is guidance for diagnosis, not a guaranteed optimum. Change one variable at a time and compare the convergence history.
Choose a mixing mode suited to the system
The current pw.x input reference describes the available modes as follows:
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
plain: charge-density Broyden mixing.TF: simple Thomas–Fermi screening for highly homogeneous systems.local-TF: screening that depends on local density, for highly inhomogeneous systems.
For slab geometries and elongated cells, the troubleshooting guide identifies local-TF as a potentially better way to damp charge sloshing. Its suitability depends on the system; it is a setting to compare, not a universal fix.
Adjust the mixing history with memory in mind
mixing_ndim is the number of iterations used by the mixing scheme. The input reference lists a default of 8; the troubleshooting guide says increasing it beyond that may help but costs memory. The reference also says it may be lowered to around 4 when memory is tight. A larger value is not a free speedup.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Investigate the documented ultrasoft-pseudopotential cutoff issue
The troubleshooting guide describes a specific issue with ultrasoft pseudopotentials (USPP): negative charge-density regions associated with augmentation pseudization or finite-cutoff truncation may impede convergence. In that case, raising ecutrho will usually help. This remedy is tied to the described USPP density behavior; it is not evidence that ecutrho explains every SCF failure.
Separate diagonalization trouble from SCF mixing trouble
When symptoms point to the eigensolver rather than charge-density oscillation, consider the diagonalization method. The current input reference identifies Davidson, diagonalization='david', as the default: “Davidson iterative diagonalization with overlap matrix (default). Fast, may in some rare cases fail.” It describes conjugate-gradient diagonalization, 'cg', as much slower, less memory-intensive, and a little more robust. Use it when there is evidence of diagonalization trouble or a memory constraint—not as the default response to charge sloshing.
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Do not confuse the inner diagonalization threshold with the SCF convergence threshold. The reference lists diago_thr_init defaults of 1.D-2 when starting from a superposition of atomic orbitals and 1.D-5 when starting from a charge density for SCF calculations; the threshold tightens automatically as self-consistency approaches convergence, never below 1.D-13. By contrast, conv_thr is defined in terms of estimated energy error and is extensive.
Diagnose cannot bracket Ef on its own terms
This message has several possible causes and should not automatically be treated as a mixing failure. The troubleshooting guide lists serious input problems such as an incorrect electron count, too few bands, or absurd broadening. Check those along with smearing and k-point sampling. With very few k-points, first-order Methfessel–Paxton smearing can also cause difficulty; Gaussian or cold smearing are documented alternatives.
There is a separate band-structure case. When calculating selected high-symmetry lines, the message may mean occupations and Fermi energy are incorrect even though the eigenvalues and eigenvectors are valid. For that case, the guide says removing occupations='tetrahedra' removes the message. Do not mistake this special situation for a general failed SCF cycle.
Choose the next change from the observed symptom
| Observed pattern | What to compare |
|---|---|
| Occupation instability or likely metallic character | Occupation method, empty-band count, broadening, and k-point sampling. |
| Oscillatory density or charge sloshing | mixing_beta, mixing_mode, and possibly mixing_ndim, accounting for memory use. |
| Slab or elongated geometry with charge sloshing | Whether local-TF is suitable for damping the oscillation. |
| USPP density behavior described above | Whether the cutoff-related issue applies and whether ecutrho warrants investigation. |
| Diagonalization failure or limited memory | Davidson versus conjugate gradient, weighing speed, robustness, and memory. |
The official documentation offers these comparison axes but does not establish a universally best setting or a benchmark across materials. A useful troubleshooting run changes one relevant factor at a time, so the convergence history can show which adjustment actually helped.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
